RESEARCH I. (continued 2)

The nitrate of ammoniac should never be decomposed in a metallic vessel,[95] nor the gas produced suffered to come in contact with any metallic surface; for in this case the free nitric acid will be decomposed, and in consequence, a certain quantity of nitrous gas produced.

The apparatus that has been generally employed in the medical pneumatic institution, for the production of nitrous oxide, consists

1. Of a glass retort, of the capacity of two or three quarts, orificed at the top, and furnished with a ground stopper.

2. Of a glass tube, conical for the purpose of receiving the neck of the retort; about ,4 inches wide in the narrowest part, 4 feet long, curved at the extremity, so as to be capable of introduction into an airholder, and inclosed by tin plate to preserve it from injury.

3. Of airholders of Mr. Watt’s invention, filled with water saturated with nitrous oxide.

4. Of a common air-furnace, provided with dampers for the regulation of the heat.

The retort, after the insertion of the salt, is connected with the tube, carefully luted, and exposed to the heat of the furnace, on a convenient stand. The temperature is never suffered to be above 500°. After the decomposition has proceeded for about a minute, so that the gas evolved from the tube enlarges the flame of a taper, the curved end is inserted into the airholder, and the nitrous oxide preserved.

The water thrown out of the airholders in consequence of the introduction of the gas, is preserved in a vessel adapted for the purpose, and employed to fill them again; for if common water was to be employed in every experiment, a great loss of gas would be produced from absorption.

A pound of fibrous nitrate of ammoniac, decomposed at a heat not above 500°, produces nearly 5 cubic feet of gas; whilst from a pound of compact nitrate of ammoniac, rarely more than 4,25 cubic feet can be collected.

For the production of nitrous oxide in quantities not exceeding 20 quarts, a mode still more simple than that I have just described may be employed. The salt may be decomposed by the heat of an argands lamp, or a common fire, in a tubulated glass retort, of 20 or 30 cubic inches in capacity, furnished with a long neck, curved at the extremity; and the gas received in small airholders.

Thus, if the pleasurable effects, or medical properties of the nitrous oxide, should ever make it an article of general request, it may be procured with much less time, labor, and expence,[96] than most of the luxuries, or even necessaries, of life.

DIVISION IV.

EXPERIMENTS and OBSERVATIONS on the COMPOSITION of NITROUS GAS, and on its ABSORPTION by different bodies.

I. Preliminaries.

In my account of the composition of nitric acid, in Division I. I gave an estimation of the quantities of oxygene and nitrogene combined in nitrous gas: I shall now detail the experiments on which that estimation is founded.

At an early period of my researches relating to nitrous oxide, from the observation of the phænomena taking place during the production of this substance, I had concluded, that the common opinion with regard to the composition of nitrous gas, was very distant from the truth. I had indeed analysed nitrous gas, by converting it into nitrous oxide, before I attempted to ascertain its composition by immediately separating the constituent principles from each other: and my first hopes of the possibility of effecting this, were derived from Dr. Priestley’s experiments on the combustion of pyrophorus in nitrous gas, and on the changes effected in it, by heated iron and charcoal.

This great philosopher found, that pyrophorus placed in contact with nitrous gas, burnt with great vividness, whilst the gas was diminished in volume to about one half, which generally consisted of nitrogene and nitrous oxide. He likewise found, iron heated by a lens in nitrous gas, increased in weight, whilst the gas was diminished about ½, and converted into nitrogene.[97]

He heated common charcoal, and charcoal of copper,[98] in nitrous gas by a lens. When common charcoal was employed, the gas was neither increased or diminished in bulk, but wholly converted into nitrogene; when charcoal of copper was used, the volume was a little increased, and the gas remaining consisted of ⁵/₇ nitrogene, and ²/₇ carbonic acid.

In his experiments on the iron and pyrophyrus, the nitrous gas was evidently decomposed. From the great quantity of nitrogene produced in those on the charcoal, it seems likely that both the common charcoal,[99] and the charcoal of copper employed contained atmospherical air, which being dispelled by the heat of the lens, was decomposed by the nitrous gas: indeed, till I made the following experiment, I suspected that the carbonic acid produced, when the charcoal of copper was employed, arose from a decomposition of the nitrous acid, formed in this way.

I introduced a piece of well-burnt charcoal, which could hardly have weighed the eighth of a grain, whilst red hot, under a cylinder filled with mercury, and admitted to it half a cubic inch of nitrous gas. A slight absorption took place.

The sun being very bright, I kept the charcoal in the focus of a small lens for near a quarter of an hour. At the end of this time the gas occupied a space nearly as before the experiment, and a very minute portion of the charcoal had been consumed. On introducing into the cylinder a small quantity of solution of strontian, a white precipitation was perceived, and the gas slowly diminished to about three tenths of a cubic inch. To these three tenths a little common air was admitted, when very slight red fumes were perceived.

This experiment convinced me, that the attraction of charcoal for the oxygene of nitrous gas, at high temperatures, was sufficiently strong to effect a slow decomposition of it.

To be more accurately acquainted with this decomposition, and to learn the quantities of carbonic acid and nitrogene produced from a known quantity of nitrous gas, I proceeded in the following manner.

II. Analysis of Nitrous Gas by Charcoal.

A quantity of nitrous gas was procured in a water apparatus, from the decomposition of nitrous acid by mercury. A portion of it was transferred to the mercurial trough. After the mercury and the jar had been dried by bibulous paper, 40 measures of this portion were agitated in a solution of sulphate of iron. The gas remaining after the absorption was complete, filled about a measure and half; so that the nitrous gas contained nearly ¹/₂₆ nitrogene.

Thermometer being 53°, a small piece of well-burnt charcoal, the weight of which could hardly have equalled a quarter of a grain, was introduced ignited, into a small cylinder filled with mercury, graduated to,10 grain measures; to this, 16 measures, equal to 160 grain m. of nitrous gas, were admitted. An absorption of about one measure and half took place. When the focus of a lens was thrown on the charcoal, a slight increase of the gas was produced, from the emission of that which had been absorbed.

After the process had been carried on for about a half an hour, the charcoal evidently began to fume, and to consume very slowly, though no alteration in the volume of the gas was observed.

The sun not constantly shining, the progress of the experiment was now and then stopped: but taking the whole time, the focus could not have been applied to it for less than four hours. When the process was finished, the gas was increased in bulk nearly three quarters of a measure.

A drop of water was introduced into the cylinder, by means of a small glass tube, on the supposition that the carbonic acid, and nitrogene, might be capable of holding in solution, more water than that contained in the nitrous gas decomposed; but no alteration of volume took place.

When 20 grain measures of solution of pale green[100] sulphate of iron were introduced into the cylinder, they became rather yellower than before, but not dark at the edges, as is always the case when nitrous gas is present. On agitation, a diminution of nearly half a measure was produced, doubtless from the absorption of some of the carbonic acid by the solution.

A small quantity of caustic potash, much more than was sufficient to decompose the sulphate of iron, was now introduced. A rapid diminution took place, and the gas remaining filled about 8 measures. This gas was agitated for some time over water, but no absorption took place. Two measures of it were then transferred into a detonating cylinder with two measures of oxygene. The electric spark was puffed through them, but no diminution was produced. Hence it was nitrogene, mingled with no ascertainable quantity of hydrogene: consequently little or no water could have been decomposed in the process.

Now supposing, for the greater ease of calculation, each of the measures employed, cubic inches.

16 of nitrous gas—¹/₂₆ = 15,4 were decomposed, and these weigh, making the necessary corrections, 5,2; but 7,4 nitrogene were produced, and these weigh about 2,2. So that reasoning from the relative specific gravities of nitrous gas and nitrogene, 5,2 grains of nitrous gas will be composed of 3 oxygene, and 2,2 nitrogene.

But 8,7 of carbonic acid were produced, which weigh 4,1 grains, and consist of 2,9 oxygene, and 1,2 charcoal.[101] Consequently, drawing conclusions from the quantity of carbonic acid formed, 5,2 grains of nitrous gas will consist of 2,9 oxygene, and 2,3 nitrogene.

The difference in these estimations is much less than could have been expected; and taking the mean proportions, it would be inferred from them, that 100 grains of nitrous gas, contain 56,5 oxygene, and 43,5 nitrogene.

I repeated this experiment with results not very different, except that the increase of volume was rather greater, and that more unabsorbable gas remained; which probably depended on the decomposition of a minute quantity of water, that had adhered to the charcoal in passing through the mercury.

As nitrous gas is decomposable into nitrous acid, and nitrogene, by the electric spark; it occurred to me, that a certain quantity of nitrous acid might have been possibly produced, in the experiments on the decomposition of nitrous gas, by the intensely ignited charcoal. To ascertain this circumstance, I introduced into 12 measures of nitrous gas, a small piece of charcoal which had been just reddened. The sun being very bright, the focus of the lens was kept on it for rather more than an hour and quarter. In the middle of the process it began to fume and to sparkle, as if in combustion. In three quarters of an hour, the gas was increased rather more than half a measure; but no alteration of volume took place afterwards.

The mercury was not white on the top as is usually the case when nitrous acid is produced. On introducing into the cylinder a little pale green sulphate of iron, and then adding prussiate of potash, a white precipitate only was produced. Now, if the minutest quantity of nitric acid had been formed, it would have been decomposed by the pale green oxide of iron, and hence, a visible quantity of prussian blue[102] produced, as will be fully explained hereafter.

III. Analysis of Nitrous Gas by Pyrophorus.

I placed some newly made pyrophorus, about as much as would fill a quarter of a cubic inch, in a jar filled with dry mercury, and introduced to it, four cubic inches of nitrous gas, procured from mercury and nitric acid.

It instantly took fire and burnt with great vividness for some moments.

After the combustion had ceased, the gas was diminished about three quarters of a cubic inch. The remainder was not examined; for the diminution appeared to go on for some time, after; in an half hour, when it was compleat, it was to 2 cubic inches. A taper, introduced into these, burnt with an enlarged flame, blue at the edges; from whence it appeared, that they were composed of nitrogene and nitrous oxide.

I now introduced about half a cubic inch of pyrophorus to two cubic inches of nitrous gas; the combustion took place, and the gas was rapidly diminished to one half; and on suffering it to remain five minutes to one third nearly; which extinguished flame.

Suspecting that this great diminution was owing to the absorption of some of the nitrogene formed, by the charcoal of the pyrophorus, I carefully made a quantity of pyrophorus; employing more than two thirds of alumn, to one third of sugar.

To rather more than half of a cubic inch of this, two cubic inches of nitrous gas, which contained about ¹/₄₀ nitrogene, were admitted. After the combustion, the gas remaining, apparently filled a space equal to 1,2 cubic inches; but, as on account of the burnt pyrophyrus in the jar, it was impossible to ascertain the volume with nicety, it was carefully and wholly transferred into another jar. It filled a space equal to 1,15 cubic inches nearly.

When water was admitted to this gas no absorption took place. It underwent no diminution with nitrous gas, and a taper plunged into it was instantly extinguished. We may consequently conclude that it was nitrogene.

Now 2 cubic inches of nitrous gas weigh,686 grains, and 1,1 of nitrogene—,05, the quantity previously contained in the gas = to 1,05, 3,19. Hence,686 of nitrous gas would be composed of,367 oxygene, and ,319 nitrogene; and 100 grains would contain 53,4 oxygene, and 46,6 nitrogene.

IV. Additional observations on the combustion of bodies in Nitrous Gas, and on its Composition.

Though phosphorus may be fused, and even sublimed, in nitrous gas, without producing the slightest luminous appearance,[103] yet when it is introduced into it in a state of active inflammation, it burns with almost as much vividness as in oxygene.[104] Hence it is evident, that at the heat of ignition, phosphorus is capable of attracting the oxygene from the nitrogene of nitrous gas.

I attempted to analise nitrous gas, by introducing into a known quantity of it, confined by mercury, phosphorus, in a vessel containing a minute quantity of oxygene.[105] The phosphorus was inflamed with an ignited iron wire, by which, at the moment of the combustion, the vessel containing it was raised from the mercury into the nitrous gas. But after making in this way, five of six unsuccessful experiments, I desisted. When the communication between the vessels was made before the oxygene was nearly combined with the phosphorus, nitrous acid was formed, which instantly destroyed the combustion; when, on the contrary, the phosphorus was suffered to consume almost the whole of the oxygene, it was not sufficiently ignited when introduced, to decompose the nitrous gas.

In one experiment, indeed, the phosphorus burnt for a moment in the nitrous gas; the diminution however was slight, and not more than ¼ of it was decomposed.

Sulphur, introduced in a state of vivid inflammation, into nitrous gas, was instantly extinguished.

I passed a strong electric shock through equal parts of hydrogene and nitrous gas, confined by mercury in a detonating tube; but no inflammation, or perceptible diminution, was produced.

19,2 grain measures of hydrogene were fired by the electric shock, with 10 of nitrous oxide, and 6 of nitrous gas; the diminution was to 17; and pale green sulphate of iron admitted to the residuum, was not discolored. Consequently the nitrous gas was decomposed by the hydrogene, and as will be hereafter more clearly understood, nearly as much nitrogene furnished by it, as would have been produced from half the quantity of nitrous oxide.

Suspecting that phosphorated hydrogene might inflame with nitrous gas, I passed the electric spark through 1 measure of phosphorated hydrogene, and 4 of nitrous gas; but no diminution was perceptible. I likewise passed the electric spark through 1 of nitrous gas, with 2 of phosphorated hydrogene, without inflammation.

Perhaps if I had tried many other different proportions of the gases, I should have at last discovered one, in which they would have inflamed; for, as will be seen hereafter, nitrous oxide cannot be decomposed by the compound combustible gases, except definite quantities are employed.

From Dr. Priestley’s experiments on iron and pyrophorus, and from the experiments I have detailed, on charcoal, phosphorus, and hydrogene, it appears that at certain temperatures, nitrous gas is decomposable by most of the combustible bodies: even the extinction of sulphur, when introduced into it in a state of inflammation, depends perhaps, on the smaller quantity of heat produced by the combustion of this body, than that of most others.

The analysis of nitrous gas by charcoal, as affording data for determining immediately the quantities of oxygene and nitrogene, ought to be considered as most accurate; and correcting it by mean calculations derived from the decomposition of nitrous gas by pyrophorus and hydrogene, and its conversion into nitrous oxide, a process to be described hereafter, we may conclude, that 100 grains of nitrous gas are composed of 55,95 oxygene, and 44,05 nitrogene; or taking away decimals, of 56 oxygene, and 44 nitrogene.

This estimation will agree very well with the mean proportions that would be given from Dr. Priestley’s experiments on the decomposition of nitrous gas by iron; but as he never ascertained the purity of his nitrous gas,[106] and probably employed different kinds in different experiments, it is impossible to fix on any one, from which accurate conclusions can be drawn.

Lavoisier’s estimation of the quantities of oxygene and nitrogene entering into the composition of nitrous gas, has been generally adopted. He supposes 64 parts of nitrous gas to be composed of 43½ of oxygene, and 20½ of nitrogene.[107]

The difference between this account and mine is very great indeed; but I have already, in Division 1st, pointed out sources of error in the experiments of this great man, on the decomposition of nitre by charcoal; which experiments were fundamental, both to his accounts of the constitution of nitrous acid, and nitrous gas.

V. Of the absorption of Nitrous Gas by Water.

Amongst the properties of nitrous gas noticed by its great discoverer, is that of absorbability by water.

In exposing nitrous air to distilled water, Dr. Priestley found a diminution of the volume of gas, nearly equal to one tenth of the bulk of the water; and by boiling the water thus impregnated, he procured again a certain portion of the nitrous gas.

Humbolt, in his paper on eudiometry, mentions the diminution of nitrous gas by water. This diminution, he supposes to arise from the decomposition of a portion of the nitrous gas, by the water, and the consequent formation of nitrate of ammoniac.[108]

I confess, that even before the following experiments were made, I was but little inclined to adopt this opinion: the small diminution of nitrous gas by water, and the uniform limits of this diminution, rendered it extremely improbable.

a. To ascertain the quantity of nitrous gas absorbable by pure water, and the limits of absorption, I introduced into a glass retort about 5 ounces of water, which had been previously boiled for some hours. The neck of the retort was inverted in mercury, and the water made to boil. After a third of it had been distilled, so that no air could possibly remain in the retort, the remainder was driven over, and condensed in an inverted jar filled with mercury. To three cubic inches of this water,[109] confined in a cylinder graduated to,05 cubic inches, 5 cubic inches of nitrous gas, containing nearly one thirtieth nitrogene, were introduced.

After agitation for near an hour, rather more than ⁴/₂₀ of a cubic inch appeared to be absorbed; but though the process was continued for near two hours longer, no further diminution took place.

The remaining gas was introduced into a tube graduated to,02 cubic inches. It measured ¹⁴/₅₀; hence ¹¹/₅₀ had been absorbed.

Consequently, 100 cubic inches of pure water are capable of absorbing 11,8 of nitrous gas. In the water thus impregnated with nitrous gas I could distinguish no peculiar taste;[110] it did not at all alter the color of blue cabbage juice.

b. To determine if the absorption of nitrous gas was owing, to a decomposition of it by the water, as Humbolt has supposed, or to a simple solution; I procured some nitrous gas from nitrous acid and mercury, containing about one seventieth nitrogene. ,5 cubic inches of it, mingled with ,25, of oxygene, from sulphuric acid and manganese left a residuum of,03. 5 cubic inches more were introduced to 3 of water, procured in the same manner as in the last experiment, in the same cylinder. After the diminution was complete, the cylinder was transferred in a small vessel containing mercury, into a water bath, and nearly covered by the water.

As the bath was heated, small globules of gas were given out from the impregnated water, and when it began to boil, the production of gas was still more rapid. After an hour’s ebullition, the volume of heated gas was equal to 1,4 cubic inches nearly.

The cylinder was now taken out of the bath, and quickly rendered cool by being placed in a water apparatus. At the common temperature the gas occupied, as nearly as possible, the space of,5 cubic inches: these,5 mingled with,25 of oxygene, of the same kind as that employed before, left a residuum nearly equal to,03.

From this experiment, which was repeated with nearly the same results, it is evident,

1. That nitrous gas is not decomposable by pure water.

2. That the diminution of volume of nitrous gas placed in contact with water, is owing to a simple solution of it in that fluid.

3. That at the temperature of 212°, nitrous gas is incapable of remaining in combination with water.

Humbolt’s opinion relating to the decomposition of nitrous gas by water, is founded upon the disengagement of vapor from distilled water impregnated with nitrous gas, by means of lime, which became white in the proximity of the muriatic acid. But this is a very imperfect, and fallacious test, of the presence of ammoniac. I have this day, April 2, 1800, heated 4 cubic inches of distilled water, impregnated with nitrous gas, with caustic lime; the vapor certainly became a little whiter when held over a vessel containing muriatic acid; but the vapor of distilled water produced precisely the same appearance,[111] which was owing, most likely, to the combination of the acid with the aqueous vapor. Indeed, when I added a particle of nitrate of ammoniac, which might have equalled one twentieth of a grain, to the lime and impregnated water, the increased whiteness of the vapor was but barely perceptible, though this quantity of nitrate of ammoniac is much more considerable than that which could have been formed, even supposing the nitrous gas decomposed.

VI. Of the absorption of Nitrous Gas by Water of different kinds.

In agitating nitrous gas over spring water, the diminution rarely amounts to more than one thirtieth, the volume of water being taken as unity. I at first suspected that this great differcnce in the quantity of gas absorbed by spring water, and pure water, depended on carbonic acid contained in the last, diminishing the attraction of it for nitrous gas: but by long boiling a quantity of spring water confined by mercury, I obtained from it about one twentieth of its bulk of air, which gave nearly the same diminution with nitrous gas, as atmospheric air.

This fact induced me to refer the difference of diminution to the decomposition of the atmospheric air held in solution by the water, the oxygene of which I supposed to be converted into nitric acid, by the nitrous gas, whilst the nitrogene was liberated; and hence the increased residuum.

a. I exposed to pure water, that is, water procured by distillation under mercury, nitrous gas, containing a known quantity of nitrogene. After the absorption was complete, I found the same quantity of nitrogene in the residuum, as was contained in a volume of gas equal to the whole quantity employed.

b. Spring water boiled for some hours, and suffered to cool under mercury, absorbed a quantity of nitrous gas equal to one thirteenth of its bulk; which is not much less than that absorbed by pure water.

c. I exposed to spring water, 10 measures of nitrous gas; the composition of which had been accurately ascertained; the diminution was one twenty-eighth, the volume of water being taken as unity. On placing the residuum in contact with solution of sulphate of iron, the nitrogene remaining was nearly one twentieth more than had been contained by the gas before its exposure to water.

d. Distilled water was saturated with common air, by being agitated for some time in the atmosphere. Nitrous gas placed in contact with this water, underwent a diminution of ¹/₁₈; the volume of water being unity. The gas remaining after the absorption contained about one twenty-seventh nitrogene more than before.

e. Nitrous gas exposed to water combined with about one fourth of its volume of carbonic acid, diminished to ¹/₃₂[112] nearly. The remainder contained little or no superabundant nitrogene.

From these observations it appears, that the different degrees of diminution of nitrous gas by different kinds of water, may depend upon various causes.

1. Less nitrous gas will be absorbed by water holding in solution earthy salts, than by pure water; and in this case the diminution of the attraction of water for nitrous gas will probably be in the ratio of the quantities of salt combined with it. a. b.

2. The apparent diminution of nitrous gas in water, holding in solution atmospheric air, will be less than in pure water, though the absolute diminution will be greater; for the same portion will be absorbed, whilst another portion is combined with the oxygene of the atmospheric air contained in the water; and from the disengagement of the nitrogene of this air, arises an increased residuum. c. d.

3. Probably in waters containing nitrogene, hydrogene, and other gases, absorbable only to a slight extent, the apparent diminution will be less, on account of the disengagement of those gases from the water, by the stronger affinity of nitrous gas for that fluid.

4. In water containing carbonic acid, and probably some other acid gases, the diminution will be small in proportion to the quantity of gas contained in the water: the affinity of this fluid for nitrous gas being diminished by its greater affinity for the substance combined with it. e.

The different diminution of nitrous gas when agitated in different kinds of water, has been long observed by experimenters on the constituent parts of the atmosphere, and various solutions have been given of the phænomenon; the most singular is that of Humbolt.[113] He supposes that the apparent diminution of nitrous gas is less in spring water than distilled water, on account of the decomposition of the carbonate of lime contained in the spring water, by the nitrous acid formed from the contact of nitrous gas with the water; the carbonic acid disengaged from this decomposition increasing the residuum.

This opinion may be confuted without even reference to my observations. It is, indeed, altogether unworthy of a philosopher, generally acute and ingenious. He seems to have forgotten that carbonic acid is absorbable by water.

VII. Of the absorption of Nitrous Gas, by solution of pale green Sulphate of Iron.

a. The discovery of the exact difference between the sulphates of iron, is owing to Proust.[114] According to the ingenious researches of this chemist, there exist two varieties of sulphate of iron, the green and the red. The oxide in the green sulphate contains ²⁷/₁₀₀ oxygen. This salt, when pure, is insoluble in spirit of wine; its solution in water is of a pale green color; it is not altered by the gallic acid, and affords a white precipitate with alkaline prussiates.

The red sulphate of iron is soluble in alcohol and uncrystalizable; its oxide contains ⁴⁸/₁₀₀ oxygene. It forms a black precipitate with the gallic acid, and with the alkaline prussiates, a blue one.

The common sulphates of iron generally consist of combinations of these two varieties in different proportions.

The green sulphate may be converted into the red by oxygenated muriatic acid or nitric acid. The common sulphate may be converted into green sulphate, by agitation in contact with sulphurated hydrogene.

The green sulphate has a strong affinity for oxygene, it attracts it from the atmosphere, from oxygenated marine acid, and nitric acid. The alkalies precipitate from it a pale green oxide, which if exposed to the atmosphere, rapidly becomes yellow red.

The red sulphate of iron has no affinity for oxygene, and when decomposed by the alkalies, gives a red precipitate, which undergoes no alteration when exposed to the atmosphere.[115]

b. The absorption of nitrous gas by a solution of sulphate of iron, was long ago discovered by Priestley. During this absorption, he remarked a change of color in the solution, analogous to that produced by the mixture of it with nitric acid.

This chemical fact has been lately applied by Humbolt, to the discovery of the nitrogene generally mingled with nitrous gas.

Vauquelin and Humbolt have published a memoir, on the causes of the absorption[116] of nitrous gas by solution of sulphate of iron. They saturated an ounce and half of sulphate of iron in solution, with 180 cubic inches of nitrous gas.

Thus impregnated it strongly reddened tincture of turnsoyle; when mingled with sulphuric acid, gave nitric acid vapor; and saturated with potash, ammoniacal vapor.

By analysis, it produced as much ammoniac as that contained in 4 grains of ammoniacal muriate, and a quantity of nitric acid equal to that existing in 17 grains of nitre. Hence they concluded, that the nitrous gas and a portion of the water of the solution, had mutually decomposed each other; the oxygene of the water combining with the oxygene and a portion of the nitrogene of nitrous gas to form nitric acid; and its hydrogene uniting with the remaining nitrogene, to generate ammoniac.

They have taken no notice of the nature of the sulphate of iron employed, which was most probably the common or mixed sulphate; nor of the attraction of the oxide of iron in this substance for oxygene.

c. Before I was acquainted with the observations of Proust, the common facts relating to the oxygenation of vitriol of iron induced me to suppose, that the attraction of this substance for oxygene was in some way connected with the process of absorption. The comparison of the experiments of Humbolt and Vauquelin, with the observations of Proust, enabled me to discover the true nature of the process.

I procured a solution of red sulphate of iron, by passing oxygenated muriatic acid through a solution of common sulphate of iron, till it gave only a red precipitate, when mingled with caustic potash. To nitrous gas confined by mercury, a small quantity of this solution was introduced. On agitation, its color altered to muddy green; but the absorption that took place was extremely trifling: in half an hour it did not amount to,2, the volume of the solution being unity, when it had nearly regained the yellow color.

I now obtained a solution of green sulphate of iron, by dissolving iron filings in diluted sulphuric acid. The solution was agitated in contact with sulphurated hydrogene, and afterwards boiled; when it gave a white precipitate with prussiate of potash.

A small quantity of this solution agitated in nitrous gas, quickly became of an olive brown, and the gas was diminished with great rapidity; in two minutes, a quantity equal to four times the volume of the solution, had been absorbed.

These facts convinced me that the solubility of nitrous gas in common sulphate of iron, chiefly depended upon the pale green sulphate contained by it; and that the attraction of one of the constituents of this substance, the green oxide of iron, for oxygene, was one of the causes of the phænomenon.

d. Green sulphate of iron rapidly decomposes nitric acid. It was consequently difficult to conceive how any affinities existing between nitrous gas, water, and green sulphate of iron, could produce the nitric acid found in the experiments of Vauquelin and Humbolt.

To ascertain if the presence of a great quantity of water destroyed the power of green sulphate of iron to decompose nitric acid, I introduced into a cubic inch of solution of green sulphate of iron, two drops of concentrated nitric acid.

The solution assumed a very light olive color; prussiate of potash mingled with a little of it, gave a dark green precipitate. Hence the nitric acid had been evidently decomposed. As no nitrous gas was given out, which is always the case when nitric acid is poured on crystalised sulphate of iron, I suspected that a compleat decomposition of the acid had taken place; but when the solution was heated, a few minute globules of gas were liberated, and it gradually became slightly clouded.

Having often remarked that no precipitation is ever produced during the conversion of green sulphate of iron into red, by oxygenated muriatic acid, or concentrated nitric acid, I could refer the cloudiness to no other cause than to the formation of ammoniac.

To ascertain if this substance had been produced, a quantity of slacked caustic lime was thrown into the solution. On the application of heat, the ammoniacal smell was distinctly perceptible, and the vapor held over orange nitrous acid, gave dense white fumes.

e. When I considered this fact of the decomposition of nitric acid and water by the solution of green sulphate of iron, and the change of color effected in it by the absorption of nitrous gas, exactly analogous to that produced by the decomposition of nitric acid; I was induced to believe that the nitric acid found in the analysis of Vauquelin and Humbolt, had been formed by the combination of some of the nitrous gas thrown into the solution with the oxygene of the atmosphere: and that the absorbability of nitrous gas, by solution of green sulphate of iron, was owing to a decomposition produced by the combination of its oxygene with the green oxide of iron, and of its nitrogene with the hydrogene disengaged from water, decompounded at the same time.

To ascertain this, I procured a quantity of nitrous gas: it was suffered to remain in contact with water for some hours after its production. Transferred to the mercurial apparatus, it gave no white vapor when placed in contact with solution of ammoniac; and consequently held no nitric acid in solution.

Into a graduated jar filled with mercury, a cubic inch of concentrated solution of pure green sulphate of iron was introduced, and 7 cubic inches of nitrous gas admitted to it. The solution immediately became dark olive at the edges, and on agitation this color was diffused through it. In 3 minutes, when near 5¾ cubic inches had been absorbed, the diminution ceased. The solution was now of a bright olive brown, and transparent at the edges. After it had rested for a quarter of an hour, no farther absorption was observed; the color was the same, and no precipitation could be perceived. A little of it was thrown into a small glass tube, under the mercury, and examined in the atmosphere. Its taste was rather more astringent than that of solution of green sulphate; it did not at all alter the color of red cabbage juice. When a little of it was poured on the mercury, it soon lost its color, its taste became acid, and it quickly reddened cabbage juice, even rendered green by an alkali.

To the solution remaining in the mercurial jar, a small quantity of prussiate of potash was introduced, to ascertain if any red sulphate of iron had been formed; but instead of the production of either a blue, or a white precipitate, the whole of the solution became opaque, and chocolate colored.

Surprised at this appearance, I was at first induced to suppose, that the ammoniac formed by the nitrogene of the nitrous gas and the hydrogene of the water, had been sufficient to precipitate from the sulphuric acid, the red oxide of iron produced, and that the color of the mixture was owing to this precipitation. To dissolve any uncombined oxide that might exist in the solution, I added a very minute quantity of diluted sulphuric acid; but little alteration of color was produced. Hence, evidently, no red oxide had been formed.

This unexpected result obliged me to theorise a second time, by supposing that nitrate of ammoniac had been produced, which by combining with the white prussiate of iron, generated a new combination. But on mingling together green sulphate of iron, prussiate of potash, and nitrate of ammoniac in the atmosphere, the mixture remained perfectly white.

To ascertain if any nitric acid existed, combined with any of the bases, in the impregnated solution, I introduced into it an equal bulk of diluted sulphuric acid: it became rather paler; but no green or blue tinge was produced.

That the prussic acid had not been decomposed, was evident from the bright green produced, when less than a grain of dilute nitric acid was admitted into the solution.

f. From these experiments it was evident, that no red sulphate of iron, or nitric acid, and consequently no ammoniac, had been produced after the absorption of nitrous gas by green sulphate of iron. And when I compared them with the observations of Priestley, who had expelled by heat a minute quantity of nitrous gas from an impregnated solution of common sulphate of iron, and who found common air phlogisticated by standing in contact with it, I began to suspect that nitrous gas was simply dissolved in the solution, without undergoing decomposition.

g. To determine more accurately the nature of the process, I introduced into a mercurial cylinder 410 grains of solution of green sulphate of iron, occupying a space nearly equal to a cubic inch and quarter; it was saturated with nitrous gas, by absorbing 8 cubic inches. This saturated solution exhibited the same appearance as the last; and after remaining near an hour untouched, had evidently deposited no oxide of iron, nor gained any acid properties.

Into a small mattrass filled with mercury, having a tight stopper with a curved tube adapted to it, the greater part of this solution was introduced; judging from the capacity of the mattrass, about 50 grains of it might have been lost. To prevent common air from coming in contact with the solution, the stopper was introduced into the mattrass under the mercury; the curved tube connected with a graduated cylinder filled with that substance; and the mattrass brought over the side of the mercurial trough. But in spite of these precautions a large globule of common air got into the top of the mattrass, from the curvature of the tube. When the heat of a spirit lamp was applied to the solution, it gave out gas with great rapidity, and gradually lost its color. When 5 cubic inches were collected it became perfectly pale green, whilst a yellow red precipitate was deposited on the bottom of the mattrass.

On pouring a little of the clear solution into prussiate of potash, it gave only white prussiate of iron.

But on introducing a particle of sulphuric acid into the solution, sufficient to dissolve some of the red precipitate, and then pouring a little of it into a solution of prussiate of potash, it gave a fine blue prussiate of iron.

Hence the red precipitate was evidently red yellow oxide of iron.

I now examined the gas, suspecting that it was nitrous oxide. On mingling a little of it with atmospheric air, it gave red vapor, and diminished. Solution of sulphate of iron introduced to the remainder, almost wholly absorbed it: the small residual globule of nitrogene could not equal one thirtieth of a cubic inch.

Consequently it was nitrous gas, nearly pure.

Caustic potash was now introduced into the solution, till all the oxide of iron was precipitated. The solution, when heated, gave a strong smell of ammoniac, and dense white fumes when held over muriatic acid. It was kept at the heat of ebullition till the evaporation had been nearly compleated. Sulphuric acid poured upon the residuum gave no yellow fumes, or nitric acid vapor in any way perceptible; even when heated and made to boil, there was no indication of the production of any vapor, except that of the sulphuric acid.

h. This experiment, compared with the others, seemed almost to prove, that nitrous gas combined with solution of pale green sulphate of iron, at the common temperature, without decomposition; and that when the impregnated solution was heated, the greater portion of gas was disengaged, whilst the remainder was decompounded by the green oxide of iron; which attracted at the same time oxygene from the water and the nitrous gas; whilst their other constituent principles, hydrogene and nitrogene, entered into union as ammoniac.

Whilst, however, I was reasoning upon this singular chemical change, as affording presumptive proofs in favor of the exertion of simple affinities by the constituent parts of compound substances, a doubt concerning the decomposition of the nitrous gas occurred to me. As near as I could guess at the quantity of nitrous gas contained by the impregnated solution, at least ¾ of it must have been expelled undecompounded.

More than a quarter of a cubic inch of common air had been present in the mattrass: the oxygene of this common air must have combined with the nitrous gas, to form nitric acid. Might not this nitric acid have been decomposed, and furnished oxygene to the red oxide of iron, and nitrogene to the small quantity of ammoniac found in the solution, as in d?

i. I now introduced to a solution of green sulphate confined by mercury, nitrous gas, perfectly free from nitric acid. When the solution was saturated, a portion of it was introduced into a small mattrass filled with dry mercury, in the mercurial trough. The curved tube was closed by a small cork at the top, and filled with nitrous gas; it was then adapted to the mattrass, which was raised from the trough, and the solution thus effectually preserved from the contact of the atmosphere.

When the heat of a spirit lamp was applied to the mattrass, it began to give out gas with great rapidity. After some time the solution lost its dark color, and became turbid. When the production of nitrous gas had ceased, it was suffered to cool. A copious red precipitate had fallen down; which, examined by the same tests as in the last experiment, proved to be red oxide of iron.

The solution treated with lime, as before, gave ammoniac; but with sulphuric acid, not the slightest indications of nitric acid.

k. Having thus procured full evidence of the decomposition of nitrous gas in the heated solution, in order to gain a more accurate acquaintance with the affinities exerted, I endeavoured to ascertain the quantity of nitrous gas decomposed by a given solution, under known circumstances.

Into a cylinder of the capacity of 20 cubic inches, inverted in mercury, 1150 grains of solution of green sulphate of iron, of specific gravity 1,4, were introduced. Nitrous gas was admitted to it, and after some time 21 cubic inches were absorbed.

The impregnated solution was thrown into a mattrass, in the same manner as in the last experiment, and the same precautions taken to preserve it from the contact of atmospheric air. A quantity was lost during the process of transferring, which, reasoning from the space occupied in the mattrass by the remaining portion, as determined by experiment afterwards, must have amounted nearly to 240 grains.

The curved tube from the mattrass was now made to communicate with the mercurial airholder. By the application of heat 12,5 cubic inches of nitrous gas were collected, after the common temperature had been restored to the mattrass; which was suffered to remain in communication with the conducting tube.

The solution was now pale green, that is, of its natural color, and a considerable quantity of red oxide of iron had been deposited.

Solid caustic potash was introduced into it, till all the green oxide of iron had been precipitated, and till the solution rendered green, red cabbage juice.

A tube was now accurately connected with the mattrass, bent, and introduced into a small quantity of diluted sulphuric acid. Nearly half of the fluid in it was slowly distilled into the sulphuric acid, by the heat of a spirit lamp. The impregnated acid evaporated at a heat above 212°, and gave a small quantity of crystalised salt, which barely amounted to two grains and quarter: it had every property of sulphate of ammoniac. Sulphuric acid in excess was poured on the residuum, and the whole distilled by a heat not exceeding 300°, into a small quantity of water. This water, after the process, tasted strongly of sulphuric acid; it had no peculiar odor. Tin thrown into it when heated, was not perceptibly oxydated; mingled with strontitic lime water, it gave a copious white precipitate, and after the precipitation became almost tasteless. Hence it evidently contained no nitric acid.

The 12,5 cubic inches of undecompounded gas that came over were examined; and accounting for the small quantity of common air previously contained in the airholder, must have been almost pure.

l. Now supposing 927 grains of the impregnated solution (including the weight of the nitrous gas), to have been operated upon, this must have contained about 16,7 cubic inches of nitrous gas. But 12,5 cubic inches escaped undecompounded: hence 4,2 were decomposed; and these weigh 1,44 grains, and are composed of,8 oxygene, and,64 nitrogene.[117]

Consequently, the nitrous gas must have furnished,8 of oxygene to the green oxide of iron.

But,64 of nitrogene require,15 of hydrogene to form,79 of ammoniac:[118] consequently 1 of water was decompounded, and this furnished,85 of oxygene to the green oxide of iron.

The green oxide of iron contains ²⁷/₁₀₀ oxygene; the red ⁴⁸/₁₀₀. But the whole quantity of oxygene supplied from the water and nitrous gas is 0,8 + 0,85 = 1,65; and calculating on the difference of the composition of the red and green oxide of iron, 5,7 grains of red oxide must have been deposited, and consequently these would saturate as much acid as,79 grains of ammoniac, or 4,1 grains of green oxide of iron.[119]

And supposing the ammoniac in sulphate of ammoniac to be to the acid as 1 is to 3,[120] 3.2 grains of sulphate of ammoniac must have been formed, containing about 2,4 grains acid; and then 6,5 grains of green sulphate of iron must have been decomposed.

Hence we gain the following equation:

6,5 green s. = 2,41 sul. acid + 4,1 gr. ox. iron.

+

1,44 nit. gas = ,64 nitrogene + ,8 oxygene.

+

1 water = ,85 oxygene, + ,15 hydrogene,

equal

3,2 sul. am. = 2,41 s. acid + ,64 nit. + ,15 hyd.

+

5,7 r. ox. iron = 4,1 gr. ox. iron + 1,6 oxyg.

Though the estimation of the quantities in this equation must not be considered as strictly accurate, on account of the degree of uncertainty that remains concerning the exact numerical expression of the quantities of the constituents of water, ammoniac, and the other compound bodies employed; yet as founded on a simple quantity, that is, the nitrous gas decomposed, it cannot be very distant from the truth.

The sulphate of ammoniac given by experiment, is considerably less than that which was really produced; much of it was probably carried off during the evaporation of the superabundant acid.

The conclusions that may be drawn from this experiment, afford a striking instance of the importance of the application of the science of quantity to the chemical changes: for the data being one chemical fact, the decomposition of a given quantity of nitrous gas by known agents; the composition of nitrous gas, of water, ammoniac, the oxides of iron, and sulphate of ammoniac; we are able not only to determine the quantities of the simple constituents that have entered into new arrangements, but likewise the composition of two compound bodies, the green and red sulphates of iron.[121]

m. Though from the experiments in e it appeared that no decomposition of nitrous gas had been produced during or even after its absorption by solution of sulphate of iron at the common temperature; yet a suspicion that it might take place slowly, and that indications of it might be given by deposition, induced me to examine minutely two impregnated solutions, one of which had been at rest, confined by mercury, for 19 hours, and the other for 27. In neither of them could I discover any deposition, or alteration of color, which might denote a change.

Two cubic inches of oxygene were admitted to half a cubic inch of one of these solutions. The oxygene was slowly absorbed, and the solution gradually lost its color.

To ascertain if during the conversion of the nitrous gas held in solution by sulphate of iron, into nitric acid, by the oxygene of the atmosphere at the common temperature, any water was decomposed; I suffered an impregnated solution, weighing nearly two ounces, to remain in contact with the atmosphere at 57°-62°, till it was become perfectly pale. It then had a strong acid taste, effervesced with carbonate of potash, and gave a blue precipitate with prussiate of potash.—It was saturated with quicklime, and heated: slight indications of the presence of ammoniac were perceived.

As in this experiment the nitric acid had been most probably decomposed by the green oxide of iron, as in f, I sent oxygenated muriatic acid through an impregnated solution, till all the green oxide of iron was converted into red, and all the nitrous gas into nitric acid.

This solution saturated with potash, and heated, gave no ammoniacal smell.

From these experiments we may conclude,

1st. That solution of red sulphate of iron has little or no affinity for nitrous gas[122]; and that solution of common sulphate absorbs nitrous gas only in proportion as it contains green sulphate.

2dly. That solutions of green sulphate of iron dissolve nitrous gas in quantities proportionable to their concentration, without effecting any decomposition of it at common temperatures. And the solubility of nitrous gas in solution of green sulphate, may be supposed to depend on an equilibrium of affinity, produced by the following simple attractions:

1. That of green oxide of iron for the oxygene of nitrous gas and water.

2. That of the hydrogene of the water for the nitrogene of the nitrous gas.

3. That of the principles of the sulphuric acid, for nitrogene and hydrogene.

3dly. That at high temperatures, that is, from 200° to 300°, the equilibrium of affinity producing the binary combination between nitrous gas and solution of green sulphate of iron is destroyed; the attraction of the green oxide of iron for oxygene being increased; whilst probably that of nitrogene for hydrogene is diminished.

Hence the nitrous gas is either liberated,[123] in consequence of the affinity between oxygene and hydrogene, and oxygene and nitrogene not following the same ratio of alteration on increased temperature; or decomposed, because at a certain temperature the green oxide exerts such affinities upon water and nitrous gas, as to attract oxygene from both of them to form red oxide; whilst the still existing affinity between the hydrogene of the one, and the nitrogene of the other, disposes them to combine to form ammoniac.

4thly. That the change of color produced by introducing nitric acid to solution of common sulphate of iron, exactly analogous to that occasioned in it by impregnation with nitrous gas, is owing to the decomposition of the acid, by the combination of its oxygene with the green oxide of iron, and of its nitrous gas with the solution.

5thly. That nitrous gas in combination with solution of green sulphate of iron, is capable of exerting a strong affinity upon free or loosely combined oxygene, and of uniting with it to form nitric acid.

n. The products obtained from a solution of sulphate of iron saturated with nitrous gas, by Vauquelin and Humbolt, and their consequent mistake with regard to the nature of the process of absorption,[124] must have arisen from exposure of their impregnated solution to the atmosphere.

Indeed, from the acidity of it, on examination, from the small portion of ammoniac, and the large quantity of nitric acid obtained, it appears most probable that the whole of the nitrous gas employed was converted into nitric acid, by combining with atmospheric oxygene; for no nitric acid could have been obtained in the mode in which they operated, unless the green oxide of iron in the solution had been previously converted into red.

VIII. On the absorption of Nitrous Gas by solution of green Muriate of Iron.

a. The analogy between the affinities of the constituents of the muriate and sulphate of iron, induced me to conjecture that they possessed similar powers of absorbing nitrous gas; and I soon found that this was actually the case; for on agitating half a cubic inch of solution of muriated iron, procured by dissolving iron filings in muriatic acid, in nitrous gas, the gas was absorbed with great rapidity, whilst the solution assumed a deep and bright brown tinge.

b. Proust,[125] who as I have before mentioned, supposes the existence of two oxides of iron only, one containing ²⁷/₁₀₀ oxygene, the other ⁴⁸/₁₀₀, has assumed, that the muriatic acid, and most other acids as well as the sulphuric, are capable of combining with these oxides, and of forming with each of them a distinct salt. He has, however, detailed no experiments on the muriates of iron.

As these salts are still more distinct from each other in their properties than the sulphates, and as these properties are connected with the phænomenon of the absorption and decomposition of nitrous gas, I shall detail the observations I have been able to make upon them.

c. When iron filings have been dissolved in pure muriatic acid, and the solution preserved from the contact of air, it is of a pale green color, and gives a white precipitate with alkaline prussiates. The alkalies throw down from it a light green oxide of iron.

When evaporated, it gives crystals almost white, which are extremely soluble in water; but insoluble in alcohol.

The solution of green muriate of iron has a great affinity for oxygene, and attracts it from the atmosphere, from nitric acid, and probably from oxygenated muriatic acid.

When red oxide of iron is dissolved in muriatic acid, or when nitric acid is decomposed by solution of green muriate of iron; the red muriate of iron is produced. The solution of this salt is of a deep brown red, its odor is peculiar, and its taste, even in a very diluted state, highly astringent. It acts upon animal and vegetable matters in a manner somewhat analogous to the oxygenated muriatic acid, rendering them yellowish white, or yellow.[126]

Sulphuric acid poured upon it, produces a smell resembling that of oxygenated muriatic acid. Evaporated at a low temperature, it gives an uncrystalisable dark, orange colored salt, which is soluble in alcohol, and when decomposed by the alkalies, gives a red precipitate. With prussiate of potash it gives prussian blue.

The common muriate of iron consists of different proportions of these two salts. It may be converted into red muriate by concentrated nitric acid, or into green by sulphurated hydrogene.

d. To ascertain if solution of red muriate of iron was capable of absorbing nitrous gas, I introduced into a jar filled with mercury, a cubic inch of nitrous gas, and admitted to it nearly half a cubic inch of solution of red muriate of iron. No discoloration took place. By much agitation, however, an absorption of nearly,2 was produced, and the solution became of a muddy green. But this change of color, and probably the absorption, was in consequence of the oxydation of either the mercury, or some imperfect metals combined with it, by the oxygene of the red muriate. For I afterwards found, that precisely the same change of color was produced when a solution was agitated over mercury.

e. I introduced to a cubic inch of concentrated solution of green muriate of iron, 7 cubic inches of nitrous gas, free from nitric acid; the solution instantly became colored at the edges, and on agitation absorbed the gas with much greater rapidity than even sulphate of iron; in a minute, only a quarter of a cubic inch remained.

The solution appeared of a very dark brown, but evidently no precipitation had taken place in it, and the edges, when viewed against the light, were transparent and puce colored.

Five cubic inches more of nitrous gas were now dissolved in the solution. The intensity of the color increased, and after an hour no deposition had taken place. A little of it was then examined in the atmosphere; it had a much more astringent taste than the unimpregnated solution, and effected no change in red cabbage juice. When prussiate of potash was introduced into it, its color changed to olive brown. A few drops of the solution, that had accidentally fallen on the mercury, soon became colorless, and then effervesced with carbonate of potash, and tasted strongly acid.

The remainder of the impregnated solution, which must have nearly equalled,75 cubic inches, was introduced into a mattrass, having a stopper and curved tube, as in the experiments on the solution of sulphate of iron; great care being taken to preserve it from the contact of air.

The mattrass was heated by a spirit lamp, the curved tube being in communication with a mercurial cylinder. Near 8 cubic inches of nitrous gas were collected, when the solution became of a muddy yellow. It was suffered to cool, and examined. A small quantity of yellow precipitate covered the bottom of the mattrass; the fluid was pellucid, and light green. A little of it thrown on prussiate of potash, gave a white precipitate, colored by streaks of light blue. When the yellow precipitate was partly dissolved by sulphuric acid, a drop of the solution, mingled with prussiate of potash, gave a deep blue green.

Hence, evidently, the precipitate was red oxide of iron.

Caustic potash in excess was introduced into the remainder of the solution, and it was heated. It gave an evident smell of ammoniac, and dense white fumes, when held over strong phlogisticated nitrous acid.

When half of it was evaporated, sulphuric acid in excess was poured on the remainder; muriatic acid was liberated, not perceptibly combined with any nitric acid.

f. In an experiment that I made to ascertain the quantity of nitrous gas capable of combining with solution of green muriate of iron; I found that,75 cubic inches of saturated solution absorbed about 18 of nitrous gas, which is nearly double the quantity combinable with an equal portion of the strongest solution of sulphate of iron. A part of this impregnated solution, heated slowly, gave out more gas in proportion to the quantity it contained, than the last, and consequently produced less precipitate; so that I am inclined to suppose it probable, that at a certain temperature, all the dissolved nitrous gas may be dispelled from a solution.

From these experiments we may conclude,

1st. That the solution of green muriate of iron absorbs nitrous gas in consequence of nearly the same affinities as solution of green sulphate of iron; its capability of absorbing larger quantities depending most probably on its greater concentration (that is, on the greater solubility of the muriate of iron), and perhaps, in some measure, on a new combining affinity, that of muriatic acid for oxygene.

2dly. That at certain temperatures nitrous gas is either liberated from solution of green muriate, or decomposed, by the combination of its oxygene with green oxide of iron, and of its nitrogene with hydrogene, produced from water decompounded by the oxide at the same time.

IX. Absorption of Nitrous Gas by Solution of Nitrate of Iron.

a. As well as two sulphates and two muriates of iron, there exist two nitrates.[127] When concentrated nitric acid is made to act upon iron, nitrous gas is disengaged with great rapidity, and with great increase of temperature: the solution assumes a yellowish tinge, and as the process goes on, a yellow red oxide is precipitated.

Nitrate of iron made in this way, gives a bright blue mingled with prussiate of potash, and decomposed by the alkalies, a red precipitate. Its solution has little or no affinity for nitrous gas.

b. When very dilute nitric acid, that is, such as of specific gravity 1,16, is made to oxydate iron, without the assistance of heat, the solution gives out no gas for some time, and becomes dark olive brown: when neutralised it gives, decomposed by the alkalies, a light green precipitate; and mingled with prussiate of potash, pale green prussiate of iron.

It owes its color to the nitrous gas it holds in solution. By exposure to the atmosphere it becomes pale, the nitrous gas combined with it being converted into nitric acid.

It is then capable of absorbing nitrous gas, and consists of pale nitrate of iron, mingled with red nitrate.

I have not yet obtained a nitrate of iron giving only a white precipitate with prussiate of potash, that is, such as contains only oxide of iron at its minimum of oxydation; for when pure green oxide of iron is dissolved by very dilute nitric acid, a small quantity of the acid is generally decomposed, which is likewise the case in the decomposition of nitre by green sulphate of iron. The solutions of nitrate of iron, however, procured in both of these modes, absorb nitrous gas with rapidity, and by sulphurated hydrogene might probably be converted into pale nitrate.

As it is impossible to obtain concentrated solutions of pale nitrate of iron, chiefly containing green oxide, its powers of absorbing nitrous gas cannot be compared with the muriatic and sulphuric solutions, unless they are made of nearly the same specific gravity.

Nitrous gas is disengaged by heat from the impregnated solution of nitrate of iron, at the same time that much red oxide of iron is precipitated. Whether any nitrous gas is decomposed, I have not yet ascertained; for when unimpregnated pale nitrate of iron is heated, a part of the acid, and of the water of the solution, is decomposed by the green oxide of iron;[128] and in consequence ammoniac, and red nitrate of iron formed, whilst red oxide is precipitated.

X. Absorption of Nitrous Gas by other Metallic Solutions.

a. White prussiate of iron in contact with water absorbs nitrous gas to a great extent, and becomes dark chocolate.[129]

b. Concentrated solution of sulphate of tin, probably at its minimum of oxydation, absorbs one eighth of its bulk of nitrous gas, and becomes brown, without deposition.

c. Solution of sulphate of zinc absorbs about one tenth of its volume of nitrous gas, and becomes green.

d. Solution of muriate of zinc[130] absorbs nearly the same quantity, and becomes orange brown.

e. These are all the metallic substances on which I have experimented. It is more than probable that there exist others possessing similar powers of absorbing nitrous gas.

Whenever the metals capable of decomposing water exist in solutions at their minimum of oxydation, the affinities exerted by them on nitrous gas and water, will be such as to produce combination. The powers of metallic solutions to combine with nitrous gas at common temperatures, as well as to decompose it at higher temperatures, will probably be in the ratio of the affinity of the metallic oxides they contain, for oxygene.

XI. The action of Sulphurated Hydrogene on solution of Green Sulphate of Iron, impregnated with Nitrous Gas.

a. In an experiment on the absorption of nitrous gas by solution of green sulphate of iron, I introduced an unboiled solution of common sulphate, deprived of red oxide of iron by sulphurated hydrogene, into a jar filled with nitrous gas; the absorption took place as usual, and nearly six of gas entered into combination, the volume of the solution being unity. On applying heat to a part of this impregnated solution, the whole of the nitrous gas it contained (as nearly as I could guess), was expelled undecompounded, and no yellow precipitate produced. Prussiate of potash poured into it gave only white prussiate of iron; and when it was heated with lime, no ammoniacal smell was perceptible.

I could refer this phænomenon to no other cause than to the existence of a small quantity of sulphurated hydrogene in the solution. That this was the real cause I found from the following experiment.

b. One part of a solution of green sulphate of iron, formed by the agitation of common sulphate of iron in contact with sulphurated hydrogene, was boiled for some minutes to expel the small quantity of gas retained by it undecompounded. It had then no peculiar smell, and gave a white prussiate of iron with prussiate of potash; the other part had a faint odor of sulphurated hydrogene, and gave a dirty white precipitate with prussiate of potash. Nearly equal quantities of each were saturated with nitrous gas, and heated. The unboiled impregnated solution gave out all its nitrous gas undecompounded; whilst in the boiled solution it was partly decomposed, yellow precipitate and ammoniac being formed.

c. This singular phænomenon of the power of a minute quantity of sulphurated hydrogene, in preventing the decomposition of nitrous gas and water, by green oxide of iron, will most probably take place in other impregnated solutions. It seems to depend on the strong affinity of the hydrogene of sulphurated hydrogene for oxygene.

XII. Additional Observations.

a. For separating nitrous gas from gases absorbable to no great extent by water; a well boiled solution of green muriate of iron should be employed. Nitrous gas agitated in this is rapidly absorbed, and it has no affinity for, or action on, nitrogene, hydrogene, or hydrocarbonate.

b. Nitrous gas carefully obtained from mercury and nitric acid, when received under mercury, or boiled water, and absorbed by solution of green muriate, or sulphate of iron, rarely leaves a residuum of ¹/₂₀₀ of its volume: preserved over common water, and absorbed, the remainder is generally from ¹/₄₀ to ¹/₉₀, from the nitrogene disengaged by the decomposition of the common air contained in the water.

c. The nitrous gas carefully obtained from the decomposition of nitric acid of 1,26, by copper, I have hardly ever found to contain more than from ¹/₃₀ to ¹/₅₀ nitrogene, when received through common water: when boiled water is employed, the residuum is nearly the same as that of nitrous gas obtained from mercury.

d. Consequently the gas from those two solutions may be used in common. It is more than probable, that the small quantities of nitrogene generally mingled with nitrous gas from copper and mercury, arise either from the common air of the vessels in which it was produced, or that of the water over which it was received. There is no reason for supposing that it is generated by a complete decomposition of a portion of the acid.[131]

e. Whenever nitrous oxide is mingled with nitrous gas and nitrogene, it must be separated by well boiled water; and after the corrections are made for the quantity of air disengaged from the water, the nitrous gas absorbed by the muriatic solution.

DIVISION V.

EXPERIMENTS and OBSERVATIONS on the production of NITROUS OXIDE from NITROUS GAS and NITRIC ACID, in different modes.

I. Preliminaries.

a.

The opinions of Priestley[132] and Kirwan,[133] relating to the causes of the conversion of nitrous gas into nitrous oxide, were founded on the theory of phlogiston. The first of these philosophers obtained nitrous oxide by placing nitrous gas in contact with moistened iron filings, or the alkaline sulphures. The last by exposing it to sulphurated hydrogene.

The Dutch chemists,[134] the latest experimentalists on nitrous oxide, have supposed that the production of this substance depends upon the simple abstraction of a portion of the oxygene of nitrous gas. They obtained nitrous oxide by exposing nitrous gas to muriate of tin, to copper in solution of ammoniac, and likewise by passing it over heated sulphur.

The diminution of volume sustained by nitrous gas during its conversion into nitrous oxide, has never been accurately ascertained; it has generally been supposed to be from two thirds to eight tenths.

b. Nitrous gas may be converted into nitrous oxide in two modes.

First, by the simple abstraction of a portion of its oxygene, by bodies possessing a strong affinity for that principle, such as alkaline sulphites, muriate of tin, and dry sulphures.

Second, by the combination of a body with a portion both of its oxygene and nitrogene, such as hydrogene, when either in a nascent form, or a peculiar state of combination.

c. Each of these modes will be distinctly treated of; and to prevent unnecessary repetitions, I shall give an account of the general manner in which the following experiments on the conversion of nitrous gas into nitrous oxide, have been conduced.

Nitrous gas, the purity of which has been accurately ascertained by solution of muriate of iron, is introduced into a graduated jar filled with dry mercury. If a fluid substance is designed for the conversion of the gas into nitrous oxide, it is heated, to expel any loosely combined air which might be liberated during the process; and then carefully introduced into the jar, by means of a small phial. After the process is finished, and the diminution accurately noted, the nitrous oxide formed is absorbed by pure water. If any nitrous gas remains, it is condensed by solution of muriate of iron; other residual gases are examined by the common tests. The quantity of nitrous oxide dissolved by the fluid is determined by a comparative experiment; and the corrections for temperature and pressure being guessed at, the conclusions drawn.

If a solid substance is used, rather more nitrous gas than that designed for the conversion, is introduced into the jar. The substance is brought in contact with the gas, by being carried under the mercury; and as a little common air generally adheres to it, a small portion of the nitrous gas is transferred into a graduated tube, after the insertion, and its purity ascertained. In other respects the process is conducted as mentioned above.

II. Of the conversion of Nitrous gas into Nitrous Oxide, by Alkaline Sulphites.

The alkaline sulphites, particularly the sulphite of potash, convert nitrous gas into nitrous oxide, with much greater rapidity than any other bodies.

At temperature 46°, 16 cubic inches of nitrous gas were converted, in less than an hour, into 7,8 of nitrous oxide, by about 100 grains of pulverised sulphite of potash, containing its water of crystalisation. No sensible increase of temperature was produced during the process, no water was decomposed, and the quantity of nitrogene remaining after the experiment, was exactly equal to that previously contained in the nitrous gas.

The nitrous oxide produced from nitrous gas by sulphite of potash, has all the properties of that generated from the decomposition of nitrate of ammoniac. It gives, as will be seen hereafter, the same products by analysis. Phosphorus, the taper, sulphur, and charcoal, burn in it with vivid light. It is absorbable by water, and capable of expulsion from it unaltered, by heat.

Nitrous gas is converted into nitrous oxide by the alkaline sulphites with the same readiness, whether exposed to the light, or deprived of its influence.

The solid sulphites act upon nitrous gas much more readily than their concentrated solutions; they should however always be suffered to retain their water of crystalisation, or otherwise they attract moisture from the gas, and render it drier, and in consequence more condensed than it would otherwise be. In case perfectly dry sulphites are employed, the gas should be always saturated with moisture after the experiment, by introducing into the cylinder a drop of water.

The sulphites, after exposure to nitrous gas, are either found wholly, or partially, converted into sulphates. Consequently the conversion of nitrous gas into nitrous oxide by these bodies, simply depends on the abstraction of a portion of its oxygene; the nitrogene and remaining oxygene assuming a more condensed state of existence.

If we reason from the different specific gravities of nitrous oxide and nitrous gas, as compared with the diminution of volume of nitrous gas, during its conversion into nitrous oxide, 100 parts of nitrous gas, supposing the former estimation of the composition of nitrous oxide given in Division III, accurate, would consist of 54 oxygene, and 46 nitrogene; which is not far from the true estimation. Or assuming the composition of nitrous gas, as given in Division IV, it would appear from the diminution, that 100 parts of nitrous oxide consisted of 38 oxygene, and 62 nitrogene.

III. Conversion of Nitrous Gas into Nitrous Oxide, by Muriate of Tin, and dry Sulphures.

a. Nitrous gas exposed to dry muriate of tin, is slowly converted into nitrous oxide: during this process the apparent diminution is to about one half; but if the products are nicely examined, and the necessary corrections made, the real diminution of nitrous gas by muriate of tin, will be the same as by the sulphites; that is, 100 parts of it will be converted into 48 of nitrous oxide.

During this conversion, no water is decomposed, and no nitrogene evolved. Solution of muriate of tin converts nitrous gas into nitrous oxide; but with much less rapidity than the solid salt.

b. Nitrous gas exposed to dry and perfectly well made sulphures, particularly such as are produced from crystalised alumn[135] and charcoal not sufficiently inflammable to burn in the atmosphere, is converted into nitrous oxide by the simple abstraction of a portion of its oxygene, and consequently undergoes a diminution of ⁵²/₁₀₀.

It is probable, that all the bodies having strong affinity for oxygene will, at certain temperatures, convert nitrous gas into nitrous oxide. Priestley, and the Dutch chemists, effected the change by heated sulphur. Perhaps nitrous gas sent through a tube heated, but not ignited, with phosphorus, would be converted into nitrous oxide.

IV. Decomposition of Nitrous Gas, by Sulphurated Hydrogene.

a. When nitrous gas and sulphurated hydrogene are mingled together, a decomposition of them slowly takes place. The gases are diminished, sulphur deposited, nitrous oxide formed, and signs of the production of ammoniac[136] and water perceived.

In this process no sulphuric, or sulphureous acid is produced; consequently none of the sulphur is oxydated, and of course the changes depend upon the combination of the hydrogene of the sulphurated hydrogene, with different portions of the oxygene and nitrogene of the nitrous gas, to form water and ammoniac, the remaining oxygene and nitrogene assuming the form of nitrous oxide.

This singular exertion of attractions by a simple body, appears highly improbable a priori, nor did I admit it, till the formation of ammoniac, and the non-oxygenation of the sulphur, were made evident by many experiments.

In those experiments, the diminution of the nitrous gas was not uniformly the same. It varied from ¹¹/₂₀ to ¹⁴/₂₀. In the most accurate of them, 5 cubic inches of nitrous gas were converted into 2.2 of nitrous oxide. Consequently the quantity of ammoniac formed was,047 grains.

In experiments on the conversion of nitrous gas into nitrous oxide, by sulphurated hydrogene, the gases should be rendered as dry as possible. The presence of water considerably retards the decomposition.

b. The sulphures[137] dissolved in water convert nitrous gas into nitrous oxide. This decomposition is not, however, produced by the simple abstraction of oxygene from the nitrous gas to form sulphuric acid. It depends as well on the decomposition of the sulphurated hydrogene dissolved in the solution, or liberated from it. In this process sulphur is deposited on the surface of the fluid, sulphuric acid is formed, and the diminution, making the necessary corrections, is nearly the same as when free sulphurated hydrogene is employed.

It is extremely probable that sulphurated hydrogene, in combination with the alkalies, as well as with water, is capable of being slowly decomposed by nitrous gas.

V. Decomposition of Nitrous Gas by Nascent Hydrogene.

a. When nitrous gas, is exposed to wetted iron filings, a diminution of its volume slowly takes place; and after a certain time, it is found converted into nitrous oxide.

In this process ammoniac[138] is formed, and the iron partially oxydated.

The water in contact with the iron is decomposed by the combination of its oxygene with that substance, and of its hydrogene with a portion of the oxygene and nitrogene of the nitrous gas, to form water and ammoniac.

That the iron is not oxydated at the expence of the oxygene of the nitrous gas, appears very probable from the analogy between this process, and the mutual decomposition of nitrous gas and sulphurated hydrogene. Besides, dry iron filings effect no change whatever in nitrous gas, at common temperatures.

I have generally found about 12 of nitrous gas converted into 5 of nitrous oxide in this process; which is not very different from the diminution by sulphurated hydrogene. It takes place equally well in light and darkness; but more rapidly in warm weather than in cold.

b. Nitrous gas exposed to a large surface of zinc, in contact with water, is slowly converted into nitrous oxide; at the same time that ammoniac is generated, and white oxide of zinc formed. This process appears to depend, like the last, upon the decomposition of water by the affinities of part of the oxygene and nitrogene of nitrous gas, for its hydrogene, to form ammoniac and water; and by that of zinc for its oxygene. Zinc placed in contact with water, and confined by mercury,[139] decomposes it at the common temperature. Zinc, when perfectly dry, does not in the slightest degree act upon nitrous gas.

I have not been able to determine exactly the diminution of volume of nitrous gas, during its conversion into nitrous oxide by zinc. In one experiment 20 measures of nitrous gas, containing about,03 nitrogene, were diminished to 9, after an exposure of eight days to wetted zinc; but from an accident, I was not able to ascertain the exact quantity of nitrous oxide formed.

c. It is probable that most of the imperfect metals will be found capable of oxydation, by the decomposition of water, when its hydrogene is attracted by the oxygene and nitrogene of nitrous gas. I have this day (April 14, 1800), examined two portions of nitrous gas, one of which had been exposed to copper filings, and the other to powder of tin, for twenty-three days.

The gas that had been exposed to copper was diminished nearly two fifths. The taper burnt in it with an enlarged flame, blue at the edges. Hence it evidently contained nitrous oxide.

The nitrous gas in contact with tin had undergone a diminution of one fourth only, and did not support flame.

VI. Miscellaneous Observations on the conversion of Nitrous Gas into Nitrous Oxide.

a. Dr. Priestley found nitrous gas exposed to a mixture of iron filings and sulphur, with water, converted after a certain time, into nitrous oxide. Sulphurated hydrogene is always produced during the combination of iron and sulphur, when they are in contact with water; and by the hydrogene of this in the nascent state, the nitrous gas is most probably decomposed.

b. Green oxide of iron moistened with water, exposed to nitrous gas, slowly gains an orange tinge, whilst the gas is diminished. Most likely it is converted into nitrous oxide; but this I have not ascertained.

c. I exposed nitrous gas, to the following bodies over mercury for many days, without any diminution, or apparent change in its properties. Alcohol, saccharine matter, hydrocarbonate, sulphureous acid, and phosphorus.

d. Crystalised sulphate, and muriate of iron, absorb a small quantity of nitrous gas, and become dark colored on the outside; but after this absorption, (which probably depends on their water of crystalisation,) has taken place, no change is effected in the gas remaining.

e. The power of iron to decompose water being much increased by increase of temperature, nitrous gas is converted into nitrous oxide much more rapidly when placed in contact with a surface of heated iron, than when exposed to it at common temperatures. During the decomposition of nitrous gas in this way, ammoniac[140] is formed.

f. The curious experiments of Rouppe,[141] on the absorption of gases by charcoal, compared with the phænomena noticed in this Division, render it probable that hydrogene in a state of loose combination with charcoal, will be found to convert nitrous gas into nitrous oxide.

VII. Recapitulation of conclusions concerning the conversion of Nitrous Gas into Nitrous Oxide.

a. Certain bodies having a strong affinity for oxygene, as the sulphites, dry sulphures, muriate of tin, &c. convert nitrous gas into nitrous oxide, by simply attracting a portion of its oxygene; whilst the remaining oxygene enters into combination with the nitrogene, and they assume a more condensed state of existence.

b. Nitrous gas is converted into nitrous oxide by hydrogene, in a peculiar state of existence, as in sulphurated hydrogene; and that by a series of very complex affinities. Both oxygene and nitrogene are attracted from the nitrous gas by the hydrogene, in such proportions as to form water and ammoniac, whilst the remaining oxygene and nitrogene[142] assume the form of nitrous oxide.

c. Nitrous gas placed in contact with bodies, such as iron and zinc decomposing water, is converted into nitrous oxide, at the same time that ammoniac is formed. It is difficult to ascertain the exact rationale of this process. For either the nascent hydrogene produced by the decomposition of the water by the metallic substance may combine with portions of both the oxygene and nitrogene of the nitrous gas; and thus by forming water and ammoniac, convert it into nitrous oxide. Or the metallic substance may attract at the same time oxygene from the water and nitrous gas, whilst the nascent hydrogene of the water seizes upon a portion of the nitrogene of the nitrous gas to form ammoniac.

The degree of diminution, and the analogy between this process and the decomposition of nitrous gas by sulphurated hydrogene, render the first opinion most probable.

VIII. The production of Nitrous Oxide during the oxydation of Tin, Zinc, and Iron, in Nitric Acid.

a. Dr. Priestley discovered, that during the solution of tin, zinc, and iron, in nitric acid, certain portions of nitrous oxide were produced, mingled with quantities of nitrous gas, and nitrogene, varying in proportion as the acid employed was more or less concentrated.

It has long been known that ammoniac is formed during the solution of tin, zinc, and iron, in diluted nitric acid. Consequently, in these processes water is decomposed.

I had designed to investigate minutely these phænomena, so as to ascertain the quantities of water and acid decompounded, and of the new products generated. But after going through some experiments on the oxydation of tin without gaining conclusive results, the labor, and sacrifice of time they demanded, obliged me to desist from pursuing the subject, till I had completed more important investigations.

I shall detail the few observations which have occurred to me, relating to the production of nitrous oxide from metallic solutions.

b. When tin is dissolved in concentrated nitric acid, such as of 1.4, nitrous oxide is produced, mingled with generally more than twice its bulk of nitrous gas. In this process but little free nitrogene is evolved, and the tin is chiefly precipitated in the form of a white powder. If the solution, after the generation of these products, is saturated with lime, and heated, the ammoniacal smell is distinct.

When nitric acid of specific gravity 1.24, is made to act upon tin; in the beginning of the process, nearly equal parts of nitrous gas and nitrous oxide are produced; as it advances, the proportion of nitrous oxide to the nitrous gas increases: the largest quantity of nitrous oxide that I have found in the gas procured from tin is ¾, the remainder being nitrous gas and nitrogene.

When tin is oxydated in an acid of less specific gravity than 1.09, the quantities of gas disengaged are very small, and consist of nitrogene, mingled with minute portions of nitrous oxide, and nitrous gas.

Whenever I have saturated solutions of tin in nitric acid of different specific gravities, with lime, and afterwards heated them, the ammoniacal smell has been uniformly perceptible, and generally most distinct when diluted acids have been employed.

c. When zinc is dissolved in nitric acid, whatever is its specific gravity, certain quantities of nitrous oxide are produced.

Nitric acids of greater specific gravity than 1.2, act upon zinc with great rapidity, and great increase of temperature. The gases disengaged from these solutions consist of nitrous gas, nitrous oxide, and nitrogene; the nitrous oxide rarely equals one third of the whole.

When nitric acid of 1,104 is made to dissolve zinc, the gas obtained in the middle of the process consists chiefly of nitrous oxide. From such a solution I obtained gas which gave a residuum of one sixth only when absorbed by water. The taper burnt in it with a brilliant flame, and sulphur with a vivid rose-colored light.

100 grains of granulated zinc, during their solution in 300 grains of nitric acid, of 1,43, diluted with 14 times its weight of water, produced 26 cubic inches of gas. Of this gas ⁷/₃₆ were nitrous, ¹⁷/₃₆36 nitrous oxide, and the remainder nitrogene. The solution saturated with lime and heated, gave a distinct smell of ammoniac.

d. During the solution of iron in concentrated nitric acid, the gas given out is chiefly nitrous; it is however generally mingled with minute quantities of nitrous oxide. When very dilute nitric acids are made to act upon iron, by the assistance of heat, nitrous oxide is produced in considerable quantities, mingled with nitrous gas and nitrogene; the proportions of which are smaller as the process advances.[143] The fluid remaining after the oxydation and solution of iron in nitric acid, always contains ammoniac.

e. As during the solution of tin, zinc, and iron, in nitric acid, the quantity of acid is diminished in proportion as the process advances, it is reasonable to suppose that the relative quantities of the gases evolved are perpetually varying. In the beginning of a dissolution, the nitrous gas generally predominates, in the middle nitrous oxide, and at the end nitrogene.

f. During the generation of nitrous gas, nitrous oxide, and ammoniac, from the decomposition of solution of nitric acid in water, by tin, zinc, and iron, very complex attractions must exist between the constituents of the substances employed. The acid and the water are decomposed at the same time, and in proportions different as the solution is more concentrated, by the combination of their oxygene with the metallic body.

The nitrous gas is produced by the combination of the metal with ³²/₁₀₀ of the oxygene of the acid. The nitrous oxide is most probably generated by the decomposition of a portion of the nitrous gas disengaged, by the nascent hydrogene of the water decompounded; some of it may be possibly formed from a more complete decomposition of the acid.

The production of ammoniac may arise, probably from two causes; from the decomposition of the nitrous gas by the combination of the nascent hydrogene of the water, with portions of its oxygene and nitrogene at the same time; and from the union of hydrogene with nascent nitrogene liberated in consequence of a complete decomposition of part of the acid.

IX. Additional Observations on the production of Nitrous Oxide.

a. When nitric acid is combined with muriatic acid, or sulphuric acid,[144] the quantities of nitrous oxide produced from its decomposition by tin, zinc, and iron, are rather increased than diminished. The nitrous oxide obtained from these solutions is, however, never sufficiently pure for physiological experiments. It is always mingled with either nitrous gas, nitrogene, or hydrogene, and sometimes with all of them.

b. From the solutions of bismuth, nickel, lead, and copper, in diluted nitric acid, I have never obtained any perceptible quantity of nitrous oxide: the gas produced is nitrous, mingled with different portions of nitrogene. Antimony and mercury, during their solution in aqua regia, give out only nitrous gas.

Probably none of the metallic bodies, except those that decompose water at temperatures below ignition, will generate nitrous oxide from nitric acid. On cobalt and manganese I have never had an opportunity of experimenting: manganese will probably produce nitrous oxide.

c. During the solution of vegetable matters[145] in nitric acid, by heat, very minute portions of nitrous oxide are sometimes produced, always however mingled with large quantities of nitrous gas, and carbonic acid.

When nitric acid is decompounded by ether, fixed oils, volatile oils, or alcohol, towards the end of the process small quantities of nitrous oxide are produced, and sometimes sufficiently pure to support the flame of the taper.[146]

d. When green oxide of iron is dissolved in nitric acid, nitrous oxide is produced, mingled with nitrogene and nitrous gas.

e. During the conversion of green sulphate, or green muriate of iron into red, by the decomposition of dilute nitric acid, nitrous oxide is formed, mingled with different proportions of nitrous gas and nitrogene.

f. When solution of green nitrate of iron is heated, a part of the acid is decomposed, red oxide is precipitated, red nitrate formed, and impure nitrous oxide evolved.

g. When iron is introduced into a solution of nitrate of copper, the copper is precipitated in its metallic state, whilst nitrous oxide, mingled with small portions of nitrogene, is produced.[147]

Both zinc and tin precipitate copper in its metallic form from solution in the nitric acid. During these precipitations, certain quantities of nitrous oxide are generated, mingled however with larger quantities of nitrogene than that produced from decomposition by iron. In all these processes ammoniac is formed, and water consequently decomposed.

The decomposition of water and nitric acid, during the precipitation of copper from solution of nitrate of copper, by tin, zinc, and iron, depends upon the strong affinity of those metals for oxygene, and their powers of combining with a larger quantity of it than copper.

X. Decomposition of Aqua Regia by Platina, and evolution of a Gas analogous to Oxygenated Muriatic Acid, and Nitrogene.

a. De la Metherie, in his essay on different airs, has asserted that the gas produced by the solution of platina in nitro-muriatic acid, is identical with the dephlogisticated nitrous gas of Priestly. He calls it nitrous gas with excess of pure air, and affirms that it diminishes, both with nitrous gas and common air.

b. I introduced into a vessel containing 30 grains of platina, 2050 grains of aqua regia, composed of equal parts, by weight, of concentrated nitric acid of 1,43, and muriatic acid of 1,16. At the common temperature, that is, 49°, no action between the acid and platina appeared to take place. On the application of the heat of a spirit lamp, the solution gradually became yellow red, and gas was given out with rapidity. Some of this gas received in a jar filled with warm water, appeared of a bright yellow color. On agitation, the greater part of it was absorbed by the water, and the remainder extinguished flame. When it was received over mercury, it acted upon it with great rapidity, and formed on the surface a white crust.

As the process of solution advanced, the color of the acid changed to dark red, at the same time that the production of gas was much increased; more than 40 cubic inches were soon collected in the water apparatus.

Different portions of the gas were examined, it exhibited the following properties:

1. Its color was orange red,[148] and its smell exactly resembled that of oxygenated muriatic acid.

2. When agitated in boiled water, it was rapidly absorbed, leaving a residuum of rather more than one twelfth.

3. The taper burnt in it with increased brilliancy, the flame being long, and deep red at the edges.

4. Iron introduced into it ignited, burnt with a dull red light.

5. Green vegetables exposed to it were instantly rendered white.

6. It underwent no diminution, mingled with atmospheric air.

7. When mingled with nitrous gas, it gave dense red vapor, and rapid diminution.

c. From the exhibition of these properties, it was evident that the gas produced during the solution of platina in aqua regia, chiefly consisted of oxygenated muriatic acid, or of a gas highly analogous to it. It was, however, difficult to conceive how a body, by combining with a portion of the oxygene of nitro-muriatic acid, could produce from it oxygenated muriatic acid, apparently mingled with very small portions of any other gas.

d. To ascertain whether any permanent gas was produced during the ebullition of aqua regia, of the same composition as that used for the solution of the platina; I kept a large quantity of it boiling for some time, in communication with the water apparatus; the gas generated appeared to be wholly nitro-muriatic, and was absorbed as fast as produced, by the water.

e. To determine whether any nitrous oxide was mingled with the peculiar gas, as well as the nature and quantity of the unabsorbable gas, nitrous gas was gradually added to 21 cubic inches of the gas produced from a new solution, till the diminution was complete: the gas remaining equalled 2,3 cubic inches; it was unabsorbable by water, and extinguished flame.

In another experiment, when the last portions of gas from a solution were carefully received in water previously boiled, 12 cubic inches agitated in water left a residuum of 1.3; whilst the same quantity decomposed by nitrous gas, containing,02 nitrogene, left about 1.5.

Hence it appeared that the aëriform products of the solution consisted of the peculiar gas analogous to oxygenated muriatic acid, and of a small quantity of nitrogene.

f. Consequently a portion of the nitric acid of the aqua regia had been decomposed; but if it had given oxygene both to the platina and muriatic acid, the quantity of nitrogene evolved ought to have been much more considerable.

g. To ascertain if any water had been decomposed, and the nitrogene condensed in the solution by its hydrogene, to form ammoniac, I saturated a solution with lime, and heated it, but no ammoniacal smell was perceived.

h. To determine if any nitrogene had entered into chemical combination with muriatic acid and oxygene, so as to form an aëriform triple compound, analogous in its properties to oxygenated muriatic acid, I exposed some of the gas to mercury, expecting that this substance, by combining with its oxygene, would effect a complete decomposition; and this was actually the case: for the gas was at first rapidly diminished, and the mercury became oxydated; its volume, however, soon increased; and the residual gas appeared to be nitrous, mingled with much nitrogene. The exact proportions of each, from an accident, I could not determine.

This experiment was inconclusive, because the nitro-muriatic acid suspended in the peculiar gas, from which it can probably be never perfectly freed, acted in common with it upon the mercury, and produced nitrous gas: and this nitrous gas, at the moment of its production, formed nitrous acid by combining with the oxygene of the peculiar gas; and the nitrous acid generated[149] was again decomposed by the mercury; and hence nitrous gas evolved, and possibly some nitrogene.