PART I. Of MINERALS. (continued 4)

It is easy to deprive Steel of the superabundant quantity of phlogiston which constitutes it Steel, and thereby reduce it to Iron. For this purpose it need only be kept red-hot some time, observing that no matter approach it all the while that is capable of refunding to it the phlogiston which the fire carries off. The same end is still sooner obtained by cementing it with meagre hungry matters, capable of absorbing the phlogiston; such as bones calcined to whiteness, and cretaceous earths.

Steel may also be made by fusion; or Pig-iron may be converted into Steel. For this purpose the same method must be employed as was above directed for reducing Pig-iron into malleable Iron; with this difference, that, as Steel requires more phlogiston than is necessary to Iron, all the means must be made use of that are capable of introducing into the Iron a great deal of phlogiston; such as melting but a small quantity of Iron at a time, and keeping it constantly encompassed with abundance of charcoal; reiterating the fusions; taking care that the blast of the bellows directed along the surface of the metal do not remove the coals that cover it, &c. And here it must be observed, that there are some sorts of Pig-iron which it is very difficult to convert into Steel by this method, and that there are others which succeed very readily, and with scarce any trouble at all. The ores which yield the last-mentioned sort of Pig-iron are called Steel Ores. Steel made by this means must be tempered in the same manner as that made by cementation[8].

PROCESS IV.

The Calcination of Iron. Sundry Saffrons of Mars.

Take filings of Iron, in what quantity you please; put them into a broad unglazed earthen vessel; set it under the muffle of a cupelling furnace; make it red-hot; stir the filings frequently; and keep up the same degree of fire till the Iron be wholly turned into a red powder.

OBSERVATIONS.

Iron easily loses its phlogiston by the action of fire. The calx that remains after its calcination is exceeding red; which makes this be thought the natural colour of the earth of that metal. It hath accordingly been observed, that all the earths and stones which either are naturally red, or acquire that colour by calcination, are ferruginous.

The yellowish red colour which every calx of Iron hath, in whatever manner it be prepared, hath procured the name of Crocus or Saffron to every preparation of this kind. That made in the manner above directed is called in Medicine Crocus Martis astringens.

The rust produced on the surface of Iron is a sort of calx of Iron made by way of dissolution. The moisture of the air acts upon the metal, dissolves it, and robs it of some of its phlogiston. This rust is called in Medicine Crocus Martis Aperiens; because it is thought that the saline parts, by means whereof the humidity dissolves the Iron, remain united with the metal after its dissolution, and give it an aperitive virtue. The Apothecaries prepare this sort of Saffron of Mars by exposing Iron filings to the dew, till they be turned entirely to rust: which is then called Saffron of Mars by dew.

Another Saffron of Mars is also prepared in a much shorter manner, by mixing filings of Iron with pulverized Sulphur, and moistening the mixture, which after some time ferments and grows hot. It is then set on the fire; the Sulphur burns away, and the mass is kept stirring till it become a red matter. This Saffron is nothing but Iron dissolved by the Acid of Sulphur, which is known to be of the same nature with that of Vitriol; and consequently this Saffron of Mars is no way differing from Vitriol calcined to redness.

PROCESS V.

Iron dissolved by the mineral Acids.

Put any mineral Acid whatever into a matrass with some water; set the matrass on a sand-bath gently heated; drop into the vessel some filings of Iron: the phenomena which usually accompany metalline dissolutions will immediately appear. Add more filings, till you observe the Acid hath lost all sensible action upon them: then remove your matrass from the sand-bath; you will find in it a solution of Iron.

OBSERVATIONS.

Iron is very easily dissolved by all the Acids. If you make use of the Vitriolic Acid, care must be taken to weaken it with water, in case it be concentrated; because the dissolution will succeed the better. The vapours that rise on this occasion are inflammable; and if a lighted paper be held to the mouth of the matrass, especially after keeping it stopt for some time and shaking the whole gently, the sulphureous vapours take fire with such rapidity as to produce a considerable explosion; which is sometimes strong enough to burst the vessel into a thousand pieces. This solution hath a green colour, and is in fact a fluid Green Vitriol, which wants nothing but rest to make it shoot into crystals.

If you make use of the Nitrous Acid, you must cease adding more filings when the liquor, after standing still some moments, becomes turbid; for, when this Acid is impregnated with Iron to a certain degree, it lets fall some of that which it had dissolved, and becomes capable of taking up fresh filings. Thus, by constantly adding new supplies of Iron, this Acid may be made to dissolve a much greater quantity thereof than is necessary to saturate it entirely. This solution is of a russet colour, and doth not crystallize.

If the weather be not extremely cold, and the Acids have a proper degree of strength, the sand-bath is unnecessary, as the dissolution will succeed very well without it.

Iron dissolved by Acids may be separated therefrom, like all other metallic substances in the same circumstances, either by the action of fire, which carries off the Acid and leaves the Martial Earth, or by the interposition of substances which have a greater affinity than metallic substances have with Acids; that is, by Absorbent Earths and Alkaline Salts. By whatever means you separate Iron from an Acid solvent, it constantly appears, after the separation, in the form of a yellowish red powder; because it is then deprived of most of the phlogiston to which it owed its metalline form; whence it is reasonable to think, that this is the proper colour of Martial earth.

All these precipitates of Iron are true Saffrons of Mars, which, as well as those prepared by calcination, are so much the further removed from the nature of a metal, the more they are deprived of their phlogiston. Thence it comes that they are more or less soluble by Acids, and more or less attracted by the magnet: as no ferruginous earth, perfectly deprived of all inflammable matter, is at all attracted by the magnet, or soluble by Acids.

CHAP. V.

Of Tin.

PROCESS I.

To extract Tin from its Ore.

Break your Tin ore into a coarse powder, and by washing carefully separate from it all the heterogeneous matters, and ores of a different kind, that may be mixed therewith. Then dry it, and roast it in a strong degree of fire, till no more Arsenical vapour rise from it. When the ore is roasted, reduce it to a fine powder, and mix it thoroughly with twice its weight of the black flux well dried, a fourth part of its weight of clean iron filings, together with as much borax and pitch; put the mixture into a crucible; over all put Sea-salt to the thickness of four fingers, and cover the crucible close.

Set the crucible thus prepared in a melting furnace: apply at first a moderate and slow degree of fire, till the flame of the pitch, which will escape through the joint of the cover, disappear entirely. Then suddenly raise your fire, and urge it with rapidity to the degree necessary for melting the whole mixture. As soon as the whole is in fusion take the crucible out of the furnace, and separate the Regulus from the scoria.

OBSERVATIONS.

All Tin ores contain a considerable quantity of Arsenic, and no Sulphur at all, or at most very little. Hence it comes that, though Tin be the lightest of all metals, its ore is nevertheless much heavier than any other; Arsenic being much heavier than Sulphur, of which the ores of every other kind always contain a pretty large proportion. This ore is moreover very hard, and is not brought to a fine powder with so much ease as the rest.

These properties of Tin ore furnish us with the means of separating it easily by lotion, not only from earthy and stony parts, but even from the other ores which may be mixed with it. And this is of the greater advantage on two accounts, viz. because Tin cannot endure, without the destruction of a great part thereof, the degree of fire necessary to scorify the refractory matters which accompany its ore; and again because this metal unites so easily with Iron and Copper, the ores of which are pretty commonly blended with Tin ore, that, after the reduction, it would be found adulterated with a mixture of these two metals, if they were not separated from it before the fusion.

But sometimes the Iron ore confounded with that of Tin is very heavy, and is not easily pulverized; whence it comes to pass that it cannot be separated therefrom by washing only. In that case the magnet must be employed to separate it, after the ore hath been roasted.

Roasting is moreover necessary for Tin ore, in order to dissipate the Arsenic which volatilizes, calcines, or destroys one part of the Tin, and reduces the rest to a short, brittle substance, like a Semi-metal. The ore is known to be sufficiently roasted when no more fumes rise from it; when it has lost the smell of garlic; and when it does not whiten a clean plate of Iron held over it.

Tin being one of those metals which are most easily calcined, it is necessary in reducing its ore to employ such matters as may furnish it with phlogiston. In order to defend it from the contact of the air, which always accelerates the calcination of metallic substances, the mixture is to be covered with Sea salt; and the addition of pitch helps to increase the quantity of phlogiston.

PROCESS II.

The Calcination of Tin.

Into an unglazed earthen dish put the quantity of Tin you intend to calcine; melt it, and keep stirring it from time to time. Its surface will be covered with a greyish white powder: continue the calcination till all your Tin be converted into such a powder, which is the Calx of Tin.

OBSERVATIONS.

Though the calcination of metalline substances is promoted by exposing them, in powder, or in filings, to the action of fire, and by ordering it so that they may not melt, because they present a much smaller surface when melted than when unmelted; yet we have not directed this precaution to be used in calcining Tin. The reason is, this metal is so fusible that it cannot endure the degree of fire requisite to destroy its phlogiston without melting, and of course, though Tin calcines easily, the operation is nevertheless tedious, because the melted metal presents but a small surface to be acted on by the fire and the air. This inconvenience may be partly remedied, and the operation greatly expedited, by dividing the quantity of Tin to be calcined into several small parcels, and exposing them to the fire in separate vessels, so that they may not re-unite when melted, and form one single mass.

Leaf Tin cast on Nitre in actual fusion causes it to deflagrate and fulminate; and from this mixture there rises a white vapour, which is converted into flowers when it meets with any obstacle to impede its flying off entirely.

Mr. Geoffroy, who went through a course of experiments on Tin, an account whereof may be seen in the Memoirs of the Academy of Sciences, found that from the colour of the calx of that metal a judgment may be formed of its degree of purity, and nearly of the quantity and quality of the metallic substances with which it is alloyed. The experiments tried on this subject by that eminent Chymist are very curious.

He performed the calcination in a crucible, which he heated to a cherry-red, and kept up the same degree of fire from the beginning to the end of the operation. The calx which formed upon his metal, in that degree of heat, appeared like small white scales, a little reddish on the under side. He pushed it to one side as it formed, to the end that it might not cover the surface of the metal, which, like all others, requires the contact of the air to turn it into a calx.

"While he was making these calcinations, he had an opportunity of observing a curious fact, of which no body before him had ever taken notice; probably because no body had ever calcined Tin by the same method. The fact is, that during the calcination of the Tin, whether you break the pellicle which forms on the surface of the metal while in red-hot fusion, or whether you let it remain without touching it, you perceive in several places a small swell of a certain matter, which bursts and makes its way through the pellicle. This matter puffs up, grows red, at the same instant takes fire, and darts out a small whitish flame, as vivid and as brilliant as that of Zinc, when urged by a fire strong enough to sublime it into flowers. The vividness of this flame may be further compared to that of several small grains of phosphorus of urine fired and gently dropped on boiling water. From this bright flame a white vapour exhales; after which the swelled mass partly crumbles down, and turns to a light white powder, sometimes spotted with red, according to the force of the fire. After this momentary ignition, there arise stronger, more numerous, or more frequent heavings of matter, out of which issues a good deal of white fume, that may be intercepted by a cover of tin-plate or copper fitted to the crucible, and appears to be the flowers of Tin, which in some measure corrode these metals. Hence Mr. Geoffroy conjectures, with a great deal of probability, that their sublimation is promoted by a portion of Arsenic. When the crust formed by this calx comes to be too thick, or in too great a quantity, to be pushed on one side, so as to leave part of the metal uncovered, Mr. Geoffroy puts out the fire, because no more calx would be formed: the communication of the external air with the Tin in fusion being absolutely necessary thereto, as hath been already said. In this operation it is to be observed that, if the fire be too slow, neither the inflammation of the sulphureous particles, nor the white fumes that rise, will be so distinctly perceived, as when the fire is of the degree requisite to keep the crucible just of a cherry-red heat.

"Mr. Geoffroy having taken off this first calx began the calcination anew. In this second heat the buddings or heavings were more considerable, and shot up in the form of cauli-flowers; but were still composed of little scales. The thoroughly calcined portion of this vegetation was likewise white and red; and the inferior surfaces of some little bits thereof were wholly red. When these calcinations are continued, sulphureous vapours rise seemingly of another kind than those which appeared in the beginning; for all the calx made by the first heat was perfectly white: whereas in the second it begins to be spotted here and there with a tinge of black. Mr. Geoffroy was obliged to go through a course of twelve several calcinations before he could convert two ounces of Tin into a calx. He had the opportunity, during these several calcinations, to observe that after the fourth, and sometimes after the third, the red spots of the calx decrease, and the black increase; that the germinations cease; that the crust of the calx remains flat; that in the twelfth fire the Tin yields no more of this scaly crust; that towards the end the undulations of the fused metal appear no longer; and that the small remainder of calx is mixed with several very minute grains of metal, which seem much harder than Tin. Mr. Geoffroy could not collect a sufficient quantity thereof to cupel them, and satisfy himself whether or no they were Silver."

Though Tin, and all the imperfect metals in general, seem converted to a calx, and lose the metalline form, by one single calcination, and that a slight one; yet they are not wholly deprived of their phlogiston: for if the calx of Tin, for instance, prepared according to the process above delivered, be cast upon Nitre in fusion, it will make that salt deflagrate very perceptibly; a convincing proof that it still contains much inflammable matter. If therefore a calx be required absolutely free from phlogiston, this first calx must be recalcined by a more violent fire, and the calcination continued till all the phlogiston be dissipated.

"Mr. Geoffroy, being desirous of having his calx of Tin very pure and perfectly calcined, exposed once more to the action of fire the twelve portions of calx obtained by his former calcinations. But, as it would have been too tedious to re-calcine them all separately, he made four parcels of the whole, each consisting of three taken according to the order in which they were first calcined; and gave to each a fire sufficiently strong, and long enough continued, to calcine them as thoroughly as was possible. After this second calcination he found them all of a most beautiful white, except the first parcel: as that consisted of the portions obtained by the three first heats, in all of which there were scales tinged with red, it still retained a stain of carnation, though hardly perceptible. Agreeably to the general rule, the two ounces of Tin gained in weight by being thus calcined; and the increase was two drams and fifty seven grains.

"Mr. Geoffroy observes, that no Tin, but what is absolutely pure, will yield a perfectly white calx. He calcined in this manner several other parcels of Tin that were impure and variously alloyed; each of which produced a calx differently coloured, according to the nature and quantity of its alloy: whence he justly concludes, that calcination is a very good method of trying the fineness of Tin, or its degree of purity." The particulars of Mr. Geoffroy's experiments on this subject, which are very curious, may be seen in the Memoirs of the Academy for 1738.

It is proper to take notice that a man should be very cautious how he exposes himself to the vapours of Tin, because they are dangerous; this metal being very justly suspected by Chymists of containing something Arsenical.

PROCESS III.

The dissolution of Tin by Acids, The Smoking Liquor of Libavius.

Put into a glass vessel what quantity you please of fine Tin cut into little bits. Pour on it thrice as much aqua regis, compounded of two parts aqua fortis weakened with an equal quantity of very pure water, and one part Spirit of Salt. An ebullition will arise, and the Tin will be very rapidly dissolved; especially if the quantities of metal and of aqua regis be considerable.

OBSERVATIONS.

Tin is soluble by all the Acids; but aqua regis dissolves it best of any. Yet in this dissolution it comes to pass that part of the dissolved Tin precipitates of its own accord to the bottom of the vessel, in the form of a white powder. This solution of Tin is very fit for preparing the purple-coloured precipitate of Gold. For this purpose the solution of Tin must be let fall, drop by drop, into a solution of Gold. Spirit of Nitre dissolves Tin nearly as aqua regis does; but it occasions a greater quantity of calx.

If two or three parts of Oil of Vitriol be poured on one part of Tin, and if the vessel in which the mixture is made be exposed to such a degree of heat as to evaporate all the moisture, there will remain a tenacious matter sticking to the sides of the vessel. If water be poured on this matter, and it be then exposed a second time to the fire, it will dissolve entirely, excepting a small portion of a glutinous substance, which also may be dissolved in fresh Oil of Vitriol.

The Acid of Sea-salt may be combined with Tin by the following process. Mix perfectly, by trituration in a marble mortar, an amalgam of two ounces of fine Tin, and two ounces and a half of Quick-silver, with as much Corrosive Sublimate. As soon as the mixture is completed, put it into a glass retort, and distil with the same precautions as we directed to be used in preparing concentrated and smoking Acids. There will first come over into the receiver some drops of a limpid liquor, which will be soon followed by an elastic spirit that will issue out with impetuosity. At last some flowers, and a saline tenacious matter, will rise into the neck of the retort. Then stop your distillation, and pour into a glass bottle the liquor you will find in the receiver. This liquor continually exhales a considerable quantity of dense, white fumes, as long as it is allowed to have a free communication with the air.

The product of this distillation is a combination of the Acid of Sea-salt with Tin. As the affinity of Tin with this Acid is greater than that of Mercury, the Acid contained in the Corrosive Sublimate quits the Mercury, wherewith it was united, to join the Tin; which it volatilizes so as to make it rise with itself in a limpid form. We make use of the amalgam of Tin with Quick-silver, because we are thereby enabled to mix the Corrosive Sublimate perfectly therewith, as the success of the operation requires it should be.

In this experiment the Tin is volatilized, and the Acid of Sea-salt, which is exceedingly concentrated, flies off incessantly in the form of white vapours. This compound is known in Chymistry by the name of Smoking Liquor of Libavius; a name derived from its quality, and from its Inventor. Tin dissolved by Acids is easily separated from them by Alkalis. It always precipitates in the form of a white calx.

CHAP. VI.

Of Lead.

PROCESS I.

To extract Lead from its Ore.

Having roasted your Lead ore reduce it to a fine powder; mix it with twice its weight of the black flux, and one fourth of its weight of clean iron filings and borax; put the whole into a crucible capable of containing at least thrice as much; over all put Sea-salt four fingers thick; cover the crucible; lute the juncture; dry the whole with a gentle heat, and set it in a melting furnace.

Make the crucible moderately red: you will hear the Sea-salt decrepitate, and after the decrepitation a small hissing in the crucible. Keep up the same degree of fire till that be over.

Then throw in as many coals as are necessary to complete the operation entirely, and raise the fire suddenly, so as to bring the whole mixture into perfect fusion. Keep up this degree of fire for a quarter of an hour, which is time sufficient for the precipitation of the Regulus.

When the operation is finished, which may be known by the quietness of the matter in the crucible, and by a bright vivid flame that will rise from it, take the crucible out of the furnace, and separate the Regulus from the scoria.

OBSERVATIONS.

All Lead ore contains a good deal of Sulphur, which must be first separated from it by roasting: and as this kind of ore is apt to fly when first exposed to the fire, it is proper to keep it covered till it be thoroughly heated. Another precaution to be used, in roasting this ore, is not to give it too great a heat, but to keep the vessel which contains it just moderately red; because it easily turns clammy, which occasions it to stick to the vessel.

The Iron that is added, and mixed with the flux, absorbs the Sulphur which may happen to remain, even after roasting: it helps also to separate from the Lead some portions of semi-metal, especially of Antimony, which are frequently mixed with this ore.

There is no fear least the Iron mix with the Lead in fusion, and adulterate it: for these two metals are incapable of contracting any union together, when each has its metalline form.

Nor is there any reason to apprehend lest the Iron should, by its refractory quality, obstruct the fusion of the mixture; for though this metal be not fusible when alone, yet, by the union it contracts with the matters it is designed to absorb, it becomes so to such a degree as in some measure to perform, on this occasion, the office of a flux.

The government of the fire is a point of great consequence in this operation. It is necessary to apply but a moderate degree of heat at first: for, when the metallic earth of the Lead, combining with the phlogiston, acquires the metalline form, it swells up in such an extraordinary manner, that there is great danger least the matter should overflow, and run all out of the containing vessel. With a view therefore to avoid this inconvenience, we direct a very large crucible to be used. This heaving of the Lead, at the instant of its reduction, is attended with a noise like the whistling of wind.

Notwithstanding all the precautions that can be used to prevent the reduction from taking place too hastily, and so occasioning the effusion of the matter, it often happens that, on raising the fire in order to bring the mixture into fusion, the hissing suddenly begins again, and is very loud. In that case all the apertures of the furnace must immediately be shut close, in order to choak and suffocate the fire: for, if this be neglected, the matter in the crucible will swell up, make its way through the luting of the juncture, nay, push up the cover, and run over. This accident is to be apprehended during the first five or six minutes after you raise the fire in order to melt the mixture. This effusion of the matter is accompanied with a dull flame, a thick, grey and yellow smoke, and a noise like that of some boiling liquor. When you observe these several phenomena you may be sure the matter is run out of the crucible, either in the manner above described, or by making its way through some cracks in the vessel, and consequently that the operation is spoiled.

Moreover, this event infallibly follows whenever a bit of coal happens to fall into the crucible; and this is one reason why it is necessary to cover it.

You may be certain that the operation hath succeeded if the scoria be smooth when cold, and have not in part escaped through the lute; if the Lead be not dispersed in globules through the whole mass of the matter contained in the crucible, but is, on the contrary, collected at the bottom, in the form of a solid Regulus, not very shining, but of a blueish cast, and ductile. Moreover, the scoria ought, in the present case, to be hard and black, and should not appear full of holes like a sieve, except only in that part which was contiguous to the Salt.

Here it is proper to observe, that the Sea-salt doth not mix with the scoria, but floats upon it. After the operation it is black; which colour it gets, no doubt, from the charred parts of the flux. The absence of these signs shews the operation to have miscarried.

When the ore to be smelted is pyritose and refractory, it may be roasted at first with a much stronger degree of fire than is used for ores that are fusible; because the martial earth, and the unmetallic earth, which are always mixed in pyritose matters, hinder it from growing readily soft in the fire. Besides, such an ore requires a greater quantity of the black flux and of borax to be mixed with it, and a higher degree of fire to fuse it.

It is generally needless to mix iron filings with this sort of ore; because the martial earth, with which pyritose matters are always accompanied, is reduced during the operation by the help of the black flux, which for that purpose is mixed with it in a large proportion, and furnishes a quantity of iron sufficient to absorb the heterogeneous minerals mixed with the Lead.

Yet, if it should be observed that the pyrites which accompany the Lead ore are arsenical, then, as such pyrites contain but a small quantity of ferruginous earth, iron filings must be added; which are, on this occasion, so much the more necessary for absorbing the Arsenic, as this mineral remains in part confounded with the ore, is reduced to a Regulus during the operation, unites with the Lead, and destroys a great deal of it by procuring its vitrification.

The Lead obtained from such pyritose ores is commonly not very pure; it is blackish and scarce ductile; qualities communicated to it by a small mixture of Copper in the pyrites, which always contain more or less thereof. We shall presently shew the method of separating Lead from Copper.

Lead ore may also be reduced by melting it amidst coals. For that purpose first kindle a fire in the furnace in which you intend to melt your ore; then put a layer of your ore immediately upon the lighted coals, and cover it with another layer of coals.

Though the melting furnace used for this operation be capable of giving a considerable heat, yet it is necessary further to increase the force of the fire by the means of a good pair of perpetual bellows, which will produce an effect like that of a forge. The ore melts, the earth of the Lead unites with the phlogiston of the coals, and so is reduced to metal, which runs through the coals, and falls into an earthen vessel placed at the bottom of the furnace to receive it. Care must be taken to keep this vessel well filled with charcoal-dust, to the end that the Lead may be in no danger of calcination while it continues there; the charcoal-dust constantly furnishing it with phlogiston to preserve its metalline form.

The earthy and stony matters that accompany the ore are scorified by this fusion, just as they are by the other which is performed in a close vessel. With regard to the Sulphur and Arsenic, they are supposed to have been first accurately separated from the ore by roasting. This is the method commonly employed for smelting Lead ore at the works.

PROCESS II.

To separate Lead from Copper.

With luting earth and charcoal-dust make a flat vessel, widening upwards, and large enough to contain your metalline mass. Set it shelving downwards from the back towards the fore-part; and in the fore-part, at the bottom, make a little gutter communicating with another vessel of the same nature, placed near the former and a little lower. Let the mouth of the gutter within side the upper vessel be narrowed, by means of a small iron plate fixed across it, while the loam is yet soft; so as to leave a very small aperture, in the lower part of this canal, sufficient to discharge the Lead as it melts. Dry the whole by placing lighted coals around it.

When this apparatus is dry, put your mixed mass of Copper and Lead into the upper vessel: both in that, and in the other vessel, light a very gentle fire of wood or charcoal, so as not to exceed the degree of heat necessary to melt Lead. In such a degree of heat the Lead contained in the mixed mass will melt, and you will see it run out of the upper vessel into the lower; at the bottom of which it will unite into a Regulus. When in this degree of heat no more Lead flows, increase the fire a little, so as to make the vessel moderately red.

When no more will run, collect the Lead contained in the lower vessel. Melt it over again in an iron ladle, with a degree of fire sufficient to make the ladle red; throw into it a little tallow or pitch, and while it burns keep stirring the metal, in order to reduce any part of it that may be calcined. Remove the pellicle or thin crust which will form on the surface; squeeze out all the Lead it contains, and then put it to the mass of Copper left in the upper vessel. Check the fire, and in the same manner take off a second skin that will form on the surface of the Lead. Lastly, when the metal is ready to fix, take off the skin that will then appear on it. The Lead remaining after this will be very pure, and free from all alloy of Copper.

With regard to the Copper itself, you will find it in the upper vessel covered with a thin coat of Lead: and if the Lead mixed with it was in the proportion of a fourth or a fifth part only, and the fire applied was gentle and slow, it will retain nearly the same form after the operation that the mixed mass had before.

OBSERVATIONS.

Lead frequently remains mixed with Copper after the reduction of its ore, especially if the ore was pyritose. Though Copper be a much more beautiful and more ductile metal than Lead, yet the latter by being alloyed with the former is rendered eager and brittle. This bad quality is easily discovered by the eye on breaking it: for the surface of the broken part appears all granulated; whereas when it is pure it is more evenly, and resembles a congeries of solid angles. If the Lead be alloyed with a considerable quantity of Copper, its colour hath a yellowish cast.

Considering the bad qualities which Copper communicates to Lead, it is necessary to separate these two metals from each other. The method above laid down is the simplest and the best. It is founded on two properties belonging to Lead: the first is that of being much more fusible than Copper; so that it will melt and run in a degree of heat that is not capable of making the Copper even red-hot, which yet is very far from being able to melt it: the second is, that Lead, though it hath an affinity with Copper, and unites very perfectly therewith, yet is not able to dissolve it without a greater heat than the degree barely necessary to fuse Lead. Hence it comes that Lead may be melted in a Copper vessel, provided no greater degree of heat be applied than that purpose requires. But when the Lead becomes so hot as to be red, fume, and boil, it instantly begins to dissolve the Copper. For this reason, it is essential to the success of our operation that a moderate degree of heat only be applied, and no greater than is requisite to keep the Lead in fusion.

Charcoal-dust is made an ingredient in the composition of the vessels used on this occasion, in order to prevent the calcination of the Lead.

The iron plate, with which the entrance of the gutter within the upper vessel is narrowed, serves to prevent the larger pieces of Copper, which the Lead may carry along with it, from passing through: it stops them, and allows the Lead to run off alone.

But as these parcels of Copper may entirely choak the passage, care must be taken, when any happen to be stopt, to remove them from the entrance of the gutter, and push them back into the middle of the vessel. It is also necessary to observe whether or no the Lead fixes any where in the passage; and, if it does, the heat of that part must be increased, in order to melt it and make it run off.

Notwithstanding all the precautions that can be taken, to hinder the melted Lead from carrying off any Copper with it, it is impossible to prevent this inconvenience entirely; and therefore the Lead is melted over again, in order to separate the small portion of Copper with which it is still adulterated.

As Copper is much lighter than Lead, if these two metals happen to be so blended together that the Copper, without being in fusion and dissolved by the Lead, is only interposed between the parts of the melted Lead, so as to swim therein, it is then precisely in the case of a solid body plunged into a fluid heavier than itself, and must rise to the surface, like wood thrown into water. It is proper to burn some inflammable matter on this melted Lead, in order to reduce such parts thereof as are constantly calcining on its surface while it is in fusion; for without this precaution they would be taken off together with the Copper.

The Copper remaining after this separation is, as we took notice before, still mixed with a little Lead. If you desire to separate it entirely therefrom, you must put it into a cupel, and expose it under the muffle to such a degree of fire as may convert all the Lead into litharge. This cannot be so done but that some of the Copper also will be scorified by the heat of the fire, and by the action of the Lead: but as there is a very great difference between the facility and readiness with which these two metals calcine, the portion of Copper that is calcined, while the whole Lead is turning into litharge, is scarce worth considering.

The Lead, though carefully separated from the Copper by the process here delivered, is not yet absolutely pure: sometimes it is alloyed with Gold, and almost always contains some Silver. If you would free the Lead as much as possible from any mixture of these two metals, you must convert it into glass, separate the remaining bead, and afterwards reduce this glass of Lead. But, as these two perfect metals are of no prejudice to the Lead, it is not usual to separate them from it, unless they be in a sufficient proportion to defray the charge, and produce some profit besides.

When we examine by the cupel the just proportion of Gold and Silver that an ore or a mixed metalline mass will yield, we make a previous assay of the Lead to be employed in the operation, and afterwards, in our estimate, deduct a proper allowance for the quantity of fine metal due to the Lead made use of.

PROCESS III.

The Calcination of Lead.

Take what quantity of Lead you please; melt it in one or more unglazed earthen pans: a dark grey powder will be found on its surface. Keep stirring the metal incessantly till it be wholly converted into such a powder, which is the Calx of Lead.

OBSERVATIONS.

As Lead is a very fusible metal, and in that respect greatly resembles Tin, most of the observations we made on the calcination of Tin may be applied here.

In the calcination of all metals, and particularly in this of Lead, there appears a singular phenomenon which is not easily accounted for. It is this: though these matters lose a great deal of their substance, either by the dissipation of their phlogiston, or because some of the metal, perhaps, exhales in vapours, yet when the calcination is over their calces are found to be increased in weight, and this increase is very considerable. An hundred pounds of Lead, for example, converted into Minium, which is nothing but a calx of Lead brought to a red colour by continuing the calcination, are found to gain ten pounds weight; so that for an hundred pounds of Lead we have one hundred and ten pounds of Minium: a prodigious and almost incredible augmentation, if it be considered that, far from adding any thing to the Lead, we have on the contrary dissipated part of it.

To account for this phenomenon Natural Philosophers and Chymists have invented several ingenious hypotheses, but none of them entirely satisfactory. As we have no established theory to proceed upon, we shall not undertake to explain this extraordinary fact.

PROCESS IV.

To prepare Glass of Lead.

Take two parts of Litharge, and one part of pure crystalline Sand; mingle them together as exactly as possible, adding a little Nitre and Sea-salt: put this mixture into a crucible of the most solid and most compact earth. Shut the crucible with a cover that may perfectly close it.

Set the crucible thus prepared in a melting furnace; fill the furnace with coals; light the fire gradually, so that the whole may be slowly heated: then raise the fire so as to make the crucible very red, and bring the matter it contains into fusion; keep it thus melted for a quarter of an hour.

Then take the crucible out of the furnace, and break it: in the bottom thereof you will most commonly find a small button of Lead, and over it a transparent Glass, of a yellow colour nearly resembling that of amber. Separate this Glass from the little button of metal, and from the saline matters which you will find above it.

OBSERVATIONS.

Pure Lead, being exposed to a strong fire without any additament, turns to Litharge; which is a scaly sort of substance, more or less yellowish, shining, and soft to the touch. This is the first advance to the Vitrification of Lead. The large refineries of Gold and Silver by the means of Lead furnish a great quantity of this material. It is sometimes whitish, and is then called Litharge of Silver; sometimes yellow, and then bears the name of Litharge of Gold. The difference of its colour depends on the degree of fire it hath undergone, and on the metalline substances vitrified with it.

Litharge alone is very fusible, and being exposed to the fire is easily converted into glass: but this Glass of Lead, made without additament, is so active, so penetrating, and so apt to swell, that it can scarcely be made use of when pure. We are obliged in some sort to clog it, by uniting it with some vitrifiable matter that is not so subtile, such as sand; and it is for this reason, not to render the mixture more fusible, that we have directed the addition of one third part of Sand to two thirds of Litharge.

The Nitre and Sea-salt, prescribed as ingredients in the mixture, are designed to procure an equal fusion of the whole. For, as the sand is lighter and less fusible than the Litharge, it will partly rise towards the upper part of the crucible when that matter first begins to flow; in consequence whereof the contents of the upper part will be much more difficult to melt, and form a Glass much more compact than that below: but the Nitre and Sea-salt possessing the upper part of the crucible, because they are still lighter than the Sand, and being in their own nature very efficacious fluxes, on account of their great fusibility, they quickly bring about the fusion of those particles of sand, which, having escaped the action of the Litharge, may have risen unvitrified to its surface.

The most difficult thing to procure, and yet the most necessary to the success of this operation, is a crucible of earth so firm and compact as not to be penetrated by the Glass of Lead, which corrodes and makes its way through every thing.

The precaution of chusing a crucible, that shall contain a good deal more than the matter to be vitrified, is a necessary one, because Litharge and Glass of Lead are very apt to swell.

The rule to keep the crucible close shut is also indispensably necessary, to prevent any bit of charcoal, or other inflammable matter, from falling into it: for when this happens it occasions a reduction of the Lead, which is always attended with a sort of effervescence, and such a considerable heaving, that commonly most of the mixture runs over the crucible. For the same reason it is very proper, before you expose the mixture to the fire, to examine whether or no it contains any matter capable of furnishing a phlogiston during the operation; and if it does, to remove that matter with great care.

The little button of Lead, found at the bottom of the crucible after the operation, comes from a small portion of Lead that is commonly left in Litharge, unless you prepare it carefully yourself, and do not take it from the fire till you are sure of having destroyed all the Lead. Besides, this small portion of Lead can be of no prejudice to the operation, because it cannot communicate its phlogiston to the rest of the matter.

The revivifying of Litharge, of the Calx, and of the Glass of Lead, may be obtained by the same processes as the reduction of its ore.

PROCESS V.

Lead dissolved by the Nitrous Acid.

Put into a matrass some aqua fortis precipitated like that used to dissolve Silver; weaken it by mixing therewith an equal quantity of common water; set the matrass in a hot sand-bath; throw into it, little by little, small bits of Lead, till you see that no more will dissolve. Aqua fortis thus lowered will dissolve about a fourth of its weight of Lead.

There is gradually formed upon the Lead, as it dissolves, first a grey powder, and afterwards a white crust, which at last hinder the solvent from acting on the remaining part of the metal; and therefore the liquor should be made to boil, and the vessel should be shaken to remove those impediments, by which means all the Lead will be dissolved.

OBSERVATIONS.

Lead very much resembles Silver, with respect to the phenomena which attend its dissolution in Acids. For example, the Nitrous Acid must be very pure and uncontaminated with the Vitriolic or Marine Acid, to qualify it for keeping the Lead in solution: for, if it be mixed with either the one or the other of these Acids, the Lead will precipitate in the form of a white powder as fast as it dissolves; which is just the case with Silver.

If the Vitriolic Acid be mixed with the Nitrous, the precipitate will be a combination of the Vitriolic Acid with Lead; that is, a Neutral Metallic Salt, or Vitriol of Lead. If the Acid of Sea-salt be mixed therewith, the precipitate will be a Plumbum corneum; that is, a Metallic Salt resembling the Luna cornea.

When all the Lead is dissolved as above described, the liquor appears milky. If it be kept warm over the fire till little crystals begin to appear on its surface, and afterwards left to stand quiet, in a certain time there will be found at the bottom a greyish powder, which being tried on Gold is Mercurial enough to whiten it. Little globules of Quick-silver are even discernible in it.

We owe this observation, together with this manner of proving the existence of Mercury in Lead, and of procuring it from thence, to M. Grosse, who hath given an account of his process in the Memoirs of the Academy of Sciences, from whence we have copied the description of the operation in hand.

The solution being quickly poured off by inclination from the grey mercurial precipitate is still milky, and deposites another white sediment. When this second precipitate falls the liquor becomes clear and limpid, and is then of a fine yellow colour, like a solution of Gold. On this gold-coloured solution, and on the two precipitates above-mentioned, M. Grosse made several observations, the chief of which we shall here insert.

The yellow liquor affects the tongue at first with a taste of sweetness; but afterwards vellicates it very smartly, and leaves on it a strong sensation of acrimony, which continues for a long time.

Alkalis precipitate the Lead suspended in this liquor, just as they do all other metals dissolved by Acids; and this precipitate of Lead is white.

Sea-salt, or Spirit of Salt, separates the Lead from its solvent, and precipitates it, as we observed before, into a Plumbum corneum: but this precipitate differs from the Luna cornea, as being very soluble in water; whereas the Luna cornea will not dissolve in it at all; or at least dissolves therein with great difficulty, and in a very small quantity. This Plumbum corneum dissolved in water is again precipitated by the Vitriolic Acid. M. Grosse observes, that this forms an exception to the eighth column of Mr. Geoffroy's Table of Affinities; in which the Acid of Sea-salt is marked as having a greater affinity than any other Acid with Metallic substances.

Our solution of Lead is also precipitated in a white powder by several Neutral Salts; such as Vitriolated Tartar, Alum, and common Vitriol. It is by the means of double affinities that these Neutral Salts effect this precipitation.

Even pure water alone is capable of precipitating the Lead of our solution, by weakening the Acid, and thereby disabling it from keeping the metal suspended.

Lastly, as all the solutions of metals in Acids are nothing but Neutral Metallic Salts in a fluid form, so if the solution of Lead be evaporated over the fire, it will shoot into very beautiful crystals, about the bigness of hemp-seed, shaped like regular pyramids having square bases. These crystals are yellowish, and have a sweet saccharine taste: but what is most singular in them is, that, as they consist of the Nitrous Acid combined with Lead, which manifestly contains a great deal of phlogiston, they constitute a Nitrous Metallic Salt, which has the property of deflagrating in a crucible, without the addition of any other inflammable matter. It is extremely hard to dissolve this Salt in water.

The grey mercurial precipitate which whitens Gold, and in which little globules of running Mercury are perceivable, is far from being pure Mercury. This metallic substance makes but a small part thereof: for it is an assemblage, 1. of little crystals of the same nature with those afforded by the evaporated solution; 2. of a portion of the white matter, or powder, which renders the solution milky; 3. of a grey powder, which M. Grosse considers as the only mercurial part; 4. and lastly, of little particles of Lead that have escaped the action of the solvent; especially if a little more Lead than the Acid is capable of dissolving were added with a view to saturate it entirely, as in the present process.

By means of motion and heat the small parcels of Mercury may be amalgamated with the Lead.

That Mercury should be found entire and in globules in the Spirit of Nitre, which very easily dissolves that metallic substance, will not be surprizing to those who reflect that, in the present case, the Acid is saturated with Lead, with which it has a greater affinity than with Mercury; as appears by M. Geoffroy's Table of Affinities, where, in the column that hath the Nitrous Acid at top, Lead is placed above Mercury. Agreeably to this, if Lead be presented to a solution of Mercury in Spirit of Nitre, the Lead will be dissolved, and as the dissolution thereof advances the Mercury will precipitate.

Hence it appears that, in order to find any Mercury in the spontaneous precipitate of Lead dissolved by the Nitrous Acid, it is necessary that the Acid be entirely saturated with Lead; or else that portion of the Acid which remains unsaturated will dissolve the Mercury.

With regard to the white powder that renders the solution milky, and afterwards precipitates, it is nothing but a portion of the Lead, which, not being intimately united with the Acid, falls in part of its own accord. It is a sort of calx of Lead, which being exposed to the fire becomes partly glass, and partly Lead, because it still retains some of its phlogiston.

CHAP. VII.

Of Mercury.

PROCESS I.

To extract Mercury from its Ore, or to revivify it from Cinabar.

Pulverize the Cinabar from which you would extract the Mercury; with this powder mix an equal part of clean iron filings; put the mixture into a retort of glass or iron, leaving at least one third part thereof empty. Set the retort thus prepared in a sand-bath, so that its body may be quite buried in the sand, and its neck decline considerably downwards: fit on a receiver half filled with water, and let the nose of the retort enter about half an inch into the water.

Heat the vessels so as to make the retort moderately red. The Mercury will rise in vapours, which will condense into little drops, and fall into the water in the receiver. When you see that nothing more comes over with this degree of heat, increase it, in order to raise what Mercury may still be left. When all the Mercury is thus brought over, take off the receiver, pour out the water contained in it, and collect the Mercury.

OBSERVATIONS.

Mercury is never mineralized in the bowels of the earth by any thing but Sulphur; with which it forms a compound of a brownish red colour, known by the name of Cinabar.

Sometimes it is only mixed with earthy and stony matters that contain no Sulphur; but, as this metallic substance is never destitute of its phlogiston, it then has its metalline form and properties. When it is found in this condition, nothing is more easy than to separate it from those heterogeneous matters. For that purpose no more is requisite than to distil the whole with a fire strong enough to raise the Mercury in vapours. This mineral is volatile; the earthy and stony matters are fixed; and a certain degree of heat will effect a complete separation of what is volatile from what is fixed.

This is not the case when Mercury is combined with Sulphur: for this latter mineral is volatile as well as Mercury; and the compound resulting from the union of them both is also volatile: so that if Cinabar were exposed to the fire in close vessels, as it must be to save the Mercury, it would be sublimed in substance, without being decomposed at all.

In order therefore to separate these two substances from each other, we must have recourse to the interposition of some third, which hath a greater affinity with one of them than the other hath, and no affinity with that other.

Iron hath all the conditions requisite for this purpose; seeing it hath, as may be seen in the Table, a much greater affinity with Sulphur than Mercury hath, and is incapable of contracting any union with Mercury.

Iron, however, is not the only substance that may be employed on this occasion: Fixed Alkalis, Absorbent earths, Copper, Lead, Silver, Regulus of Antimony, have all, as well as Iron, a greater affinity than Mercury with Sulphur. Nay, several of these substances, namely, the saline and earthy Alkalis, as well as Regulus of Antimony, cannot contract any union with Mercury: the rest, to wit, Copper, Lead, and Silver, are indeed capable of amalgamating with Mercury; but then the union which these metals contract with the Sulphur prevents it; and even though they should unite with this metallic substance, the degree of heat to which the whole mixture is exposed would soon carry up the Mercury, and separate it with ease from those fixed substances.

In this distillation the same cautions must be observed as in all others: that is, the vessels must be slowly heated, especially if a glass retort be used; the fire must be raised by degrees, and a much stronger one applied at last than at first. This operation particularly requires a very strong degree of fire, when there is but a small quantity of Mercury left.

After the operation there remains in the retort a compound of Iron and Sulphur, which may easily be converted into a crocus, by calcining it and burning away the Sulphur.

If a Fixed Alkali be employed, a Liver of Sulphur will be found in the retort after the distillation.

If the Cinabar from which you extract the Mercury be good, you will generally obtain seven eighths of its weight in Quick-silver.

In the present operation it is not necessary to lute on the receiver, because the water, in which the nose of the retort is plunged, is sufficient to fix the Mercurial vapours. In case the Cinabar, from which you intend to separate the Mercury, be mixed with a great quantity of heterogeneous, but fixed, matters, such as earths, stones, &c. it may be separated from them by subliming it with a proper degree of heat, because it is volatile.

The vapours of Mercury are prejudicial, and may excite a salivation, tremors, and palsies; they should therefore be always avoided by such as work on this mineral.

The oldest and richest mine of Mercury is that of Almaden in Spain. It is a singular property of that mine that, though the Mercury found in it is combined with Sulphur, and in the form of Cinabar, yet no additament is required to procure the separation of these two; the earthy and stony matter, with which the particles of the ore are incorporated, being itself an excellent absorbent of Sulphur.

In the Quick-silver works carried on at this mine they make no use of retorts. They place lumps of the ore on an iron grate, which stands immediately over the furnace. The furnaces which serve for this operation are closed at the top by a sort of dome, behind which stands the shaft of a chimney that communicates with the fire-place, and gives vent to the smoke. These furnaces have in their fore-side sixteen apertures, to each of which is luted an aludel in a horizontal position, communicating with a long row of other aludels placed likewise in an horizontal direction; which aludels so connected together form one long pipe or canal, the further end whereof opens into a chamber destined to receive and condense all the mercurial vapours. These rows of aludels are supported from end to end by a terrass, which runs from the body of the building, wherein the furnaces are erected, to that where the chambers are built that perform the office of receivers.

This is a very ingenious contrivance and saves much labour, expence, and trouble, that would be unavoidable if retorts were employed.

That part of the furnace which contains the lumps of ore, serves for the body of the retort; the row of aludels for its neck; and the little chambers in which these canals terminate are actual receivers. The terrass of communication, which reaches from the one building to the other, is formed of two inclined planes, the lower edges of which, meeting in the middle of the terrass, rise from thence insensibly; the one quite to the building where the furnaces are, and the other to that which forms the recipient chambers. By this means, when any Mercury escapes through the joints of the aludels, it naturally runs down along these inclined planes, and so is collected in the middle of the terrass, where the inferior sides of the planes meeting together form a sort of canal, out of which it is easily taken up.

The celebrated M. de Jussieu having viewed the whole himself, in a journey he made to this mine, furnished us with this description of the work.

PROCESS II.

To give Mercury, by the action of Fire, the appearance of a Metalline Calx.

Put Mercury into several little glass matrasses with long and narrow necks. Stop the matrasses with a little paper, to prevent any dirt from falling into them. Set them all in one sand-bath, so that they may be surrounded with sand as high as two thirds of their length. Apply the strongest degree of heat that Mercury can bear without subliming: continue this heat without interruption, till all the Mercury be turned to a red powder. The operation lasts about three months.

OBSERVATIONS.

Mercury treated according to the process here delivered hath all the appearance of a metalline calx, but it hath no more: for, if it be exposed to a pretty strong degree of fire, it sublimes, and is wholly reduced to running Mercury, without the addition of any other inflammable matter; which proves that during this long calcination it lost none of its phlogiston.

The volatile nature of Mercury, which permits it not to bear a heat of any strength without subliming, prevents our examining all the effects that fire is capable of producing on it. Yet there is reason to believe that, as this metallic substance resembles the perfect metals in its weight, its splendour, and a brilliancy which resists all the impressions of the air without alteration, it would like them be unchangeable by the greatest force of fire, if it were fixed enough to bear it.

In order to give Mercury the form of a metalline calx, it must necessarily be exposed for about three months together, to the utmost heat it can bear without subliming, as is above directed. Boerhaave kept it digesting in a less heat for fifteen years successively, both in open and in close vessels, without observing it to suffer the least change; except that there was formed upon its surface a small quantity of a black powder, which was reduced to running Mercury by trituration alone.

Mercury thus converted to a red powder is known in chymistry and medicine by the name of Mercury precipitated per se: a title proper enough, as it is actually reduced to the form of a precipitate, and that without any additament; but very improper on the other hand, considering, that in reality this Mercury is not a precipitate, as not having been separated from any menstruum in which it was dissolved.

PROCESS III.

To dissolve Mercury in the Vitriolic Acid. Turbith Mineral.

Put Mercury into a glass retort, and pour on it thrice its weight of good Oil of Vitriol. Set the retort in a sand-bath; fit on a recipient; warm the bath by degrees till the liquor just simmer. With this heat the Mercury will begin to dissolve. Continue the fire in this degree till all the Mercury be dissolved.

OBSERVATIONS.

The Vitriolic Acid dissolves Mercury pretty well: but for this purpose the Acid must be very hot, or even boil; and then too it is a very long time before the dissolution is completed. We have directed the operation to be performed in a retort; because this solution is usually employed to make another preparation called Turbith Mineral, which requires that as much as possible of the Acid solvent be abstracted by distillation. Having therefore dissolved your Mercury in the Vitriolic Acid, if you will now prepare the Turbith, you must, by continuing to heat the retort, drive over all the liquor into the receiver, and distil till nothing remains but a white powdery matter: then break the retort; pulverize its contents in a glass mortar, and thereon pour common water, which will immediately turn the white matter of a lemon-colour; wash this yellow matter in five or six warm waters, and it will be what is called in medicine Turbith Mineral; that is, a combination of the Vitriolic Acid with Mercury, five or six grains whereof is a violent purgative, and also an emetic; qualities which it possesses in common with the Vegetable Turbith, whose name it hath therefore taken.

There rises out of the retort, both while the Mercury is dissolving, and while the solvent is abstracting, a weak Spirit of Vitriol; because a great part of the Acid remains united with the Quick-silver, which at last appears in the form of a white powder: so that, if you do not incline to save the Acid which rises on this occasion, you may, instead of drawing off the liquor in a retort, evaporate it in a glass bason set on a sand-bath, which will be much sooner done.

It is very remarkable that, on this occasion, the Mercury may be exposed, without any danger of subliming, to a much greater heat than it is capable of bearing when not combined with the Vitriolic Acid; which shews that this Acid hath the property of fixing Mercury to a certain degree.

The white matter, that remains after the evaporation of the fluid, is one of the most violent corrosives, and would prove an actual poison if taken internally. By washing it several times in warm water it is freed from a great deal of its Acid, and so considerably sweetened. The proof is this; if the water used in washing the Turbith be evaporated, there remains after the evaporation a matter in form of a Salt, that being set in a cellar runs into a liquor called Oil of Mercury, which is a powerful corrosive. Several authors further direct Spirit of Wine to be burnt on the Turbith, to sweeten it still more.

If, instead of washing the white matter that remains after the moisture is drawn off, fresh Oil of Vitriol be poured on it, and then abstracted as before; this treatment being repeated two or three times, there will at last remain in the retort a matter having the appearance of an oil, which resists the action of the fire, and cannot be desiccated: qualities which are owing to the great quantity of Acid particles thus united with the Mercury. This Oil of Mercury is one of the most violent corrosives. The Mercury may be separated therefrom, by precipitating it with an Alkali, or a metallic substance that hath more affinity than Mercury with the Vitriolic Acid: Iron, for instance, may be employed in this precipitation. Mercury thus separated from the Vitriolic Acid need only be distilled to recover the form of Quick-silver.

PROCESS IV.

To combine Mercury with Sulphur. Æthiops Mineral.

Mix a dram of Sulphur with three drams of Quick-silver, by triturating the whole in a glass mortar with a glass pestle. By degrees, as you triturate, the Mercury will disappear, and the matter will acquire a black colour. Continue the triture till you cannot perceive the least particle of running Mercury. The black matter you will then have in the mortar is known in medicine by the name of Æthiops Mineral. An Æthiops may also be made by fire in the following manner.

In a shallow unglazed earthen pan melt one part of flowers of Sulphur: add three parts of running Mercury, making it fall into the pan in the form of small rain, by squeezing it through chamoy leather. Keep stirring the mixture with the shank of a tobacco-pipe all the while the Mercury is falling: you will see the matter grow thick and acquire a black colour. When the whole is thoroughly mixed, set fire to it with a match, and let as much of the Sulphur burn away as will flame.

OBSERVATIONS.

Mercury and Sulphur unite together with great ease; cold triture alone is sufficient to join them. By this means the Mercury is reduced into exceeding small atoms, and combines so perfectly with the Sulphur that the least vestige thereof is not to be seen.

Sulphur is not the only matter which being rubbed with Mercury will destroy its form and fluidity: all fat substances that have any degree of consistence, such as the fat of animals, balsams, and resins, are capable of producing the same effect. This metallic substance, being triturated for some time in a mortar with these matters, becomes at last invisible, and communicates to them a black colour. When thus divided by the interposition of heterogeneous particles, it is said to be Killed. But Mercury doth not contract such an intimate union with these other matters as it doth with Sulphur.

The Æthiops prepared by fusion is a more perfect and accurate combination of Mercury and Sulphur than the other: for, the quantity of Sulphur directed to be used in making it being much greater than is absolutely necessary to fix the Mercury, the redundant Sulphur is destroyed by burning, and none left but what is most intimately united with the Mercury; and hindered by the union it hath contracted with that metallic substance from being so easily consumed. The Æthiops therefore, which is prepared by fusion and burning the Sulphur, contains a much greater proportion of Mercury than that which is made by simple triture; so that in Medicine it ought to be prescribed in different cases, and in smaller doses.

If no more Sulphur than is just necessary to kill the Mercury be added to it at first, it will be difficult to obtain a perfect mixture; because that quantity is very small: it is better, therefore, to employ at once the quantity above directed.

PROCESS V.

To sublime the Combination of Mercury and Sulphur into Cinabar.

Grind to powder Æthiops mineral prepared by fire. Put it into a cucurbit; fit thereto a head; place it in a sand-bath, and begin with applying such a degree of heat as is requisite to sublime Sulphur. A black matter will rise, and adhere to the sides of the vessel. When nothing more will rise with this degree of heat, raise the fire so as to make the sand and the bottom of the cucurbit red; and then the remaining matter will sublime in the form of a brownish red mass, which is true Cinabar.

OBSERVATIONS.

Æthiops Mineral requires nothing but sublimation to become true Cinabar, like that found in Quick-silver mines: but our Æthiops contains still more Sulphur than ought to be in the composition of Cinabar; for which reason we have directed the degree of fire applied at first to be no greater than that which is capable of subliming Sulphur. As Cinabar, though consisting of Mercury and Sulphur, is yet much less volatile than either of these substances alone; which probably arises from the Vitriolic Acid contained in the Sulphur; therefore, if there be any redundant Sulphur in the Æthiops, which hath not contracted an intimate union with the Mercury, it will sublime by itself in this first degree of heat. Some mercurial particles also will rise with it, and give it a black colour.

Cinabar contains no more Sulphur than about a sixth or seventh part of its weight: so that, instead of employing the common Æthiops to make it, it would be better to prepare one on purpose that should contain much less Sulphur; because too much Sulphur prevents the success of the operation by blackening the Sublimate. Indeed in whatever manner you go about it, the Cinabar always appears black at first: but when it is well prepared, and contains no more than its due proportion of Sulphur, the blackness is only external. This black coat therefore may be taken off; and then the internal part will appear of a fine red, and, if sublimed a second time, will be very beautiful.

As artificial Cinabar hath the same properties with the native, it may be decomposed by the same means: so that, if you want to extract the Mercury out of it, recourse must be had to the process above delivered for working on Cinabar ores.

PROCESS VI.

To dissolve Mercury in the Nitrous Acid. Sundry Mercurial Precipitates.

Put into a matrass the quantity of Mercury you intend to dissolve: pour on it an equal quantity of good Spirit of Nitre, and set the matrass in a sand-bath moderately heated. The Mercury will dissolve with the phenomena that usually attend the dissolutions of metals in this Acid. When the dissolution is completed let the liquor cool. You will know that the Acid is perfectly saturated, if there remain at the bottom of the vessel, notwithstanding the heat, a little globule of Mercury that will not dissolve.

OBSERVATIONS.

Mercury dissolves in the Nitrous Acid with much more facility, and in much greater quantity, than in the Vitriolic; so that it is not necessary, on this occasion, to make the liquor boil. This solution when cold yields crystals, which are a Nitrous Mercurial Salt. If you desire to have a clear limpid solution of Mercury, you must employ an aqua fortis that is not tainted with the Vitriolic or Marine Acid: for, the affinity of these two Acids with Mercury being greater than that of the Nitrous Acid, they precipitate it in the form of a white powder, when they are mixed with the solvent.

Mercury thus precipitated in a white powder, out of a solution thereof in the Spirit of Nitre, is used in Medicine. To obtain this precipitate, which is known by the name of the White Precipitate, Sea-salt dissolved in water together with a little Sal Ammoniac is used; and the precipitate is washed several times in pure water, without which precaution it would be corrosive, on account of the great quantity of the Marine Acid which it would contain.

The preparation known by the name of Red Precipitate is also obtained from our solution of Mercury in Spirit of Nitre. It is made by abstracting all the moisture of the solution, either by distillation in a retort, or by evaporation in a glass bason set on a sand-bath. When it begins to grow dry it appears like a white ponderous mass. Then the fire is made strong enough to drive off almost all the Nitrous Acid, which, being now concentrated, rises in the form of red vapours. If these vapours be catched in a receiver, they condense into a liquor, which is a very strong and vastly smoking Spirit of Nitre.

By degrees, as the Nitrous Acid is forced up by the fire, the mercurial mass loses its white colour, and becomes first yellow, and at last very red. When it is become entirely of this last colour the operation is finished. The red mass remaining is a Mercury that contains but very little Acid, in comparison of what it did while it was white: and indeed the first white mass is such a violent corrosive, that it cannot be used in Medicine; whereas, when it is become red, it makes an excellent escharotic, which those who know how to use it properly apply with very great success, particularly to venereal ulcers.

This preparation is very improperly called a Precipitate: for the Mercury is not separated from the Spirit of Nitre by the interposition of any other substance, but only by evaporating the Acid. It is also called Arcanum Corallinum.

It must be observed that Mercury, by its union with the Nitrous Acid, acquires a certain degree of fixity: for the red precipitate is capable of sustaining, without being volatilized, a stronger degree of heat than pure Mercury can; which, as we observed before, is the property of Turbith Mineral also.

PROCESS VII.

To combine Mercury with the Acid of Sea-salt. Corrosive Sublimate.

Evaporate a solution of Mercury in the Nitrous Acid till there remain only a white powder, as mentioned in our observations on the preceding process. With this powder mix as much Green Vitriol calcined to whiteness, and as much decrepitated Sea-salt, as there was Mercury in the solution. Triturate the whole carefully in a glass mortar. Put this mixture into a matrass, so that two thirds thereof may remain empty, having first cut off the neck to half its length: or instead thereof you may use an apothecary's phial. Set your vessel in a sand-bath, and put sand round it as high as the contents can reach. Apply a moderate fire at first, and raise it by slow degrees. Vapours will begin to ascend. Continue the fire in the same degree till they cease. Then stop the mouth of the vessel with paper, and increase the fire till the bottom of the sand-bath be red-hot. With this degree of heat a Sublimate will rise, and adhere to the inside and upper part of the vessel, in the form of white, semi-transparent crystals. Keep up the fire to the same degree till nothing more will sublime. Then let the vessel cool; break it, and take out what is sublimed, which is Corrosive Sublimate.

OBSERVATIONS.

In this operation the mineral Acids act, and are acted upon, in a remarkable manner. Every one of the three is at first neutralized, or united with a different basis; the Vitriolic being combined with Iron; the Nitrous with Mercury, forming therewith a Nitrous Mercurial Salt; and the Marine with its natural Alkaline basis. The Vitriolic and Nitrous Acids, which are united with metalline substances, being both stronger than the Acid of Sea-salt, strive to expel it from its basis, in order to combine with it themselves; but the Vitriolic Acid, being the strongest of the two, would take sole possession of this basis exclusive of the Nitrous, which would continue united with the Mercury, if the Marine Acid had not a greater affinity than the Nitrous with this metallic substance. This Acid therefore being expelled from its basis by the Vitriolic Acid, and so set at liberty, must unite with the Mercury, and separate the Nitrous Acid from it; which now hath no resource but to unite with the Iron deserted by the Vitriolic Acid. But as all these changes are brought about by the means of a considerable heat, and as the Nitrous Acid hath not a very firm connection with the Iron, it is driven off by the force of the fire; and this it is which we see rise in vapours during the operation. It also carries off with it some parts of the other two Acids, but in a very small quantity. After the operation therefore there remains, 1. A combination of the Vitriolic Acid with the basis of Sea-salt; that is, a Glauber's Salt: 2. A red martial earth, being that which was the basis of the Vitriol: these two substances are blended together, and remain at the bottom of the vessel because of their fixity: 3. A combination of the Marine Acid with Mercury; both of which being volatile, they ascend together into the upper part of the vessel, and there form a Corrosive Sublimate.

If we reflect on this process with attention, and recollect distinctly the affinities of the different substances employed in it, we shall perceive that it is not necessary to make use of all those matters, and that the operation would succeed though several of them were left out.

First, the Nitrous Acid may be omitted; since, as hath been shewn, it is not an ingredient in the Sublimate, but is dissipated in vapours during the operation. From an accurate mixture therefore of Vitriol, Sea-salt, and Mercury, a Corrosive Sublimate must be obtained: for as the Acid of the Vitriol will disengage the Acid of Sea-salt, the latter will be at liberty to combine with the Mercury, and so form the compound we are in quest of.

Secondly, if we make use of Mercury dissolved by the Nitrous Acid, we may omit the Vitriol; because the Nitrous Acid having a greater affinity than the Marine Acid itself with the basis of Sea-salt, and the Acid of Sea-salt having a greater affinity than the Nitrous Acid with Mercury, these two Acids will naturally make an exchange of the bases with which they are united: the Nitrous will lay hold on the basis of Sea-salt, and form a quadrangular Nitre, while the Marine Acid will join the Mercury, and with it form a Corrosive Sublimate.

Thirdly, instead of Sea-salt its Acid only may be employed; which being mixed with the solution of Mercury in the Spirit of Nitre, will, by virtue of its greater affinity with that metallic substance, separate it from the Nitrous Acid, unite with it, and form a white mercurial precipitate, which need only be sublimed to become the combination required.

Fourthly, instead of Mercury dissolved in the Nitrous Acid, Mercury dissolved by the Vitriolic Acid, or Turbith, may be used; only mixing Sea-salt therewith: for these two saline substances will mutually decompound each other, by virtue of the affinities of their Acids, and for the same reasons that Sea-salt and the Mercurial Nitrous Salt decompound each other. The Vitriolic Acid quits the Mercury with which it is combined, to unite with the basis of the Sea-salt; and the Acid of this Salt being expelled by the Vitriolic, combines with the Mercury, and consequently forms our Corrosive Sublimate. In this case a Glauber's Salt remains after the sublimation.

These several methods of preparing Corrosive Sublimate are never used, because each of them is attended with some inconvenience; such as requiring too long triture, yielding a Sublimate less corrosive than it should be, or a smaller quantity of it. We must, however, except the last; which was invented by the late Mr. Boulduc, of the Academy of Sciences, who found none of these inconveniencies attending it[9].

Corrosive Sublimate may also be made only by mixing Mercury with Sea-salt, without any additament. This may appear surprizing when we consider that, as Acids have a greater affinity with Alkalis than with metallic substances, the Acid of Sea-salt ought not to quit its basis, which is Alkaline, to unite with Mercury.

In order to explain this phenomenon it must be remembered that Sea-salt, when exposed to the fire without additament, suffers a little of its Acid to escape. Now this portion of the Marine Acid unites with the Mercury, and forms a Corrosive Sublimate. Moreover, as there is a pretty strong affinity between the Marine Acid and Mercury, this may help to detach from the Sea-salt a greater quantity of Acid than it would otherwise part with. Nevertheless, the quantity of Sublimate obtained by this means is not considerable, nor is it very corrosive.

On this occasion we must also mention another combination of the Marine Acid with Mercury; which is made by mixing that metallic substance perfectly with Sal Ammoniac, by the means of triture. Mercury, like all other metals except Gold, possesses the property of decompounding Sal Ammoniac, separating the volatile Alkali which serves it for a basis, and combining, by the help of a very gentle heat, with its Acid, which is well known to be the same with that of Sea-salt. This decomposition of Sal Ammoniac, by the metalline substances, is a full exception to the first column of Mr. Geoffroy's Table of Affinities, and is the basis of several new Medicines invented by the late Comte de la Garaye[10].

Corrosive Sublimate is the most violent and the most active of all corrosive poisons. It is never used in Medicine, but in external applications. It is a powerful escharotic; it destroys proud flesh, and cleans old ulcers: but it must be used by those only who know how to apply it properly, and requires an able hand to manage it. It is not commonly applied by itself, but mixed in the proportion of half a dram to a pound of lime-water. This mixture is yellowish, and bears the name of Aqua Phagadenica.

Water dissolves Corrosive Sublimate, but in a small quantity. If a Fixed Alkali be mixed with this solution, the Mercury precipitates in the form of a red powder. If the precipitate be procured by a Volatile Alkali, it is white; if by Lime-water, it is yellow. This Mercurial Salt dissolves pretty easily in boiling Spirit of Wine.

PROCESS VIII.

Sweet Sublimate.

Take four parts of Corrosive Sublimate; pulverize it in a glass or marble mortar; add by little and little three parts of Mercury revivified from Cinabar; triturate the whole carefully, till the Mercury be perfectly killed, so that no globule thereof can be perceived. The matter will then be grey. Put this powder into an apothecary's phial, or into a matrass, whose neck is not above four or five inches long, leaving two thirds thereof empty. Set the vessel in a sand-bath, and put sand round it to one third of its heighth. Apply a moderate fire at first; and afterwards raise it gradually till you perceive that the mixture sublimes. Keep it up to this degree till nothing more will rise, and then break the vessel. Reject, as useless, a small quantity of earth which you will find at the bottom; separate also what adheres to the neck of the vessel, and carefully collect the matter in the middle, which will be white. Pulverize it; sublime it a second time, in the same manner as before; and in the same manner separate the earthy matter left at the bottom of the vessel, and what you find sublimed into the neck. Pulverize, and sublime a third time, the white matter you last found in the middle. The white matter of this third sublimation is the Sweet Sublimate, called also Aquila Alba.

OBSERVATIONS.

The Acid of Sea-salt in the Corrosive Sublimate is very far from being perfectly saturated with Mercury; and thence comes the corrosive quality of this saline compound. But though Mercury, as appears by this combination, is capable of imbibing a much greater quantity of Acid than is necessary to dissolve it; nay, though it naturally takes up this superabundant quantity of Acid, yet it doth not follow from thence that this redundant Acid may not combine with Mercury to the point of perfect saturation, so as to lose its corrosive acidity.

This is the case in the operation here described. A fresh quantity of running Mercury is mixed with Corrosive Sublimate; and the fresh Mercury, combining with the super-abounding Acid, deprives the Sublimate of its acrimony, and forms a compound which comes much nearer the nature of a Neutral Metallic Salt.

Trituration alone is not sufficient to produce an union between the newly added Mercury and the Acid of the Corrosive Sublimate: because, generally speaking, the Acid of Sea-salt cannot dissolve Mercury without the help of a certain degree of heat, and unless it be reduced into vapours.

Thus, though the newly added Mercury becomes invisible by trituration, and seems actually combined with the Corrosive Sublimate, yet the union is not intimate. There is only an interposition of parts, but no true dissolution of the newly added Mercury by the super-abundant Acid of the Corrosive Sublimate. For this reason the mixture must be sublimed; and by this sublimation only is the true union effected. Nor is one single sublimation sufficient: no less than three are necessary to deprive the Sublimate of the corrosive quality which renders it poisonous. After the third sublimation, the Sublimate being put upon the tongue gives no considerable sensation of acrimony; nor doth it retain any more of its former activity than is requisite to make it a gentle purgative, when administered from six to thirty grains for a dose.

If a less quantity of Mercury than that above directed be mixed with the Corrosive Sublimate, the super-abundant Acid will not be sufficiently saturated; and the less Mercury is added, the more of its corrosive virtue will the Sublimate retain.

If, on the contrary, a greater quantity of Mercury be added, there will be more than the Acid can possibly dissolve, and the superfluous quantity will remain in its natural form of Quick-silver. It is better therefore to err in the excess than in the defect of the proportion of Mercury to be added; because the Corrosive Sublimate will take up no more than is necessary to dulcify it.

Part of the Acid of the Corrosive Sublimate is also dissipated in vapours during the operation; and it is necessary to allow room for these vapours to circulate, and a vent to give them passage, or else they will burst the vessels. These are our reasons for leaving an empty space in the subliming vessels, and for having their necks no more than five or six inches long.

The matter which sublimes into the neck of the vessel is always very acrid; for which reason it must be separated from the Sweet Sublimate. There remains also at the bottom of the matrass an earthy, reddish matter; which probably comes from the Vitriol employed in making the Corrosive Sublimate. This matter must likewise be rejected as useless after every sublimation.

PROCESS IX.

The Panacea of Mercury.

Pulverize some Sweet Sublimate, and sublime it in the same manner as you did thrice before. Repeat this nine times. After these sublimations it will make no impression on the tongue. Then pour on it aromatic Spirit of Wine, and set the whole in digestion for eight days. After that decant the Spirit of Wine, and dry what remains, which is the Panacea of Mercury.

OBSERVATIONS.

The great number of sublimations, which the Sweet Sublimate is made to undergo, sweeten it still more, and to such a degree that it leaves no sensation on the tongue, nor hath any purgative virtue.

The Spirit of Wine in which it is digested after all the sublimations, is designed to blunt still more the sharpness of any acid particles that may not have been sufficiently dulcified by the preceding sublimations.

As Mercury is the specific remedy for venereal disorders, sundry preparations thereof have been attempted with a view to produce different effects. Sweet Sublimate is purgative; and for that reason is not quite proper for procuring a salivation, because it carries off the humours by stool. The Panacea of Mercury, which, on the contrary, is not purgative, may raise a salivation when taken inwardly.

SECTION III.

Of Operations on the Semi-Metals.

CHAP. I.

Of Antimony.

PROCESS I.

To Separate Antimony from its Ore by Fusion.

Having drilled some small holes, of about two lines in diameter, in the bottom of a crucible, put into it your Antimonial Ore broken into little bits, about the size of a hazel nut; lute on its cover; set the crucible thus prepared in the mouth of another crucible, and close the joints with lute.

At the distance of half a foot from this compound vessel place bricks all round, so as to form a furnace; the sides of which must rise as high as the brim of the uppermost crucible.

Let the bottom of this furnace be filled with ashes, up to the top of the lower crucible, and the rest of the furnace with lighted coals. Blow the fire, if it be necessary, with bellows, till the upper crucible become red. Keep it up in this degree for about a quarter of an hour. Then take your vessels out of the furnace, and you will find the Antimony collected in the bottom of the lower crucible, having run through the holes of the upper one.

OBSERVATIONS.

The ore of Antimony is one of the most fusible: it always contains a great deal of Sulphur, and cannot sustain a fire of any force without being dissipated into vapours. It requires no additament to flux it: for it is not necessary, on this occasion, that the earthy and stony matters mixed therewith be brought to fusion. It is sufficient that the Antimonial part be melted; which, as soon as it becomes fluid, is carried by its weight to the lower part of the crucible. Thus it is separated from all heterogeneous matters; which are left in the upper crucible, while it passes through the holes in its bottom, and forms a mass in the lower.

The precaution of closing all the apertures of both crucibles is necessary, on account of the volatility of this mineral: and that the Antimony, when once melted, may not continue exposed to a great heat, it is made to run down into a vessel surrounded with ashes only, and by that means very little affected with heat; ashes being one of those solid mediums that transmit least of it.

PROCESS II.

The common Regulus of Antimony.

Reduce crude Antimony to powder. Mix it with three fourths of its weight of white Tartar, and half its weight of refined Salt-petre, both pulverized. Into a large crucible made red-hot in the fire, throw a spoonful of your mixture, and cover it. There will be a very considerable detonation. When it is over, throw in a second spoonful of your mixture, and cover the crucible as before: this will produce a second detonation. Go on thus, till you have thrown in all your mixture.

When the whole has thus fulminated, increase the fire so as to bring the matter into fusion; that being done, take the crucible out of the furnace, and immediately pour its contents into an iron cone heated and greased with tallow. Strike the floor and the cone some gentle blows with a hammer, to make the Regulus precipitate: and when the matter is fixed and cold, invert the cone and turn it out. You will see it consist of two distinct substances; the uppermost of which is a saline scoria, and the undermost the reguline part. Strike this mass a blow with a hammer, in the place where these substances join, and you will by this means separate the scoria from the Regulus; the latter of which will have the form of a metallic cone, on whose base you will observe the signature of a bright star.

OBSERVATIONS.

Antimony, though separated by a former fusion from the earthy and stony parts of its ore, must nevertheless be still considered as an ore, on account of the great quantity of Sulphur it contains, which mineralizes the metalline part or Regulus. Therefore, if you desire to have this Regulus pure, you must separate it from the Sulphur that is combined with it. This may be done several ways. The method above proposed is one of the readiest and easiest, though not altogether free from inconveniencies, as we shall shew.

The Salt-petre in the mixture detonates by means of the Sulphur of the Antimony, which it consumes, and from which it separates the reguline part: but lest it should also consume some of the phlogiston which gives the Regulus its metalline form, Tartar is added; because it contains a great deal of inflammable matter, and so is capable of furnishing enough for the detonation of the Nitre, or rather for restoring to the metallic earth of the Antimony, the phlogiston that may be consumed by the Nitre.

If we consider what passes in this operation we shall soon be convinced that a great deal must be lost in it, and that we do not thereby obtain near the whole of the Regulus that the Antimony is capable of yielding: for, 1. the Regulus of Antimony being a volatile substance, much of it must be dissipated during the detonation; and so much the more as the detonation is frequently repeated, and continued for a considerable time. The flowers that may be collected by presenting cold bodies to the smoke that rises in the operation, and which may be reduced to a Regulus by the addition of a phlogiston, sufficiently prove what is here advanced.