Part 3 / Book 4 — Lecture VII. - Salts in Water

EXPERIMENTS IN CONSORT UPON THE Solution of Salts IN WATER. Read before the Royal Society, January, 18. 1676/7.

CHAP. I.

In which is shewed, the Compleat or Utmost Impregnation of WATER with several kinds of Salt, both together, and apart.

N discourse upon a Lecture formerly read, concerning the Lixivial Salts of Plants; It was mentioned, as a thing asserted by some Phylosophers, That Water having been fully impregnated with one kind of Salt, so as to bear no more of that kind; it would yet bear, or dissolve some portion of another; and so of a third. And it was referred to Me by this Honourable Chair, to examine and produce the Experiment. The doing whereof brought into my mind divers other Experiments hereunto relating.

2. §. As next, With what difference of quantity this Superimpregnation would be made, upon the Solution of different Salts?

3. §. Thirdly, Whether the Solution of a smaller quantity of several Salts, doth consist with the non-increase of the bulk of the Water? Because this also is affirmed by some.

4. §. Fourthly, What quantity of the several kinds of Salt, may be dissolved severally, in the same quantity of Water?

5. §. Fifthly, Whether by dissolving a Salt in Water, there be any Space gained, or not? That is, whether the Bulk of the Water be greater, before the Salt lying in it be fully dissolved, than it is afterwards? Or if a Cubick Inch of Salt be dissolved in nine Cubick Inches of Water; Whether the Water will then fill a Vessel of ten Cubick Inches content?

6. §. Sixthly, Whether the Space be equally gained, by an equal encrease of the same Salt?

7. §. Seventhly, Whether upon the Solution of several kinds of Salts, be gained so many several quantities of Space? That is, if the Solution of common Salt gains, suppose, an Inch, whether the Solution of Salt Armoniack gains as much, or more, or less? and so for other Salts.

8. §. Eighthly, What that just space may be, which any Salt gaineth with respect to its own Bulk, or that of the Water?

9. §. And first, for the Superimpregnation of Water; I put into a bottle ℥ij of fair Water; adding thereto, first half an Ounce of Nitre; and afterwards more, as the Water would dissolve it; and (that I might be sure the Impregnation was full) some portion above what the Water would bear. Then having separated this remaining portion; I put to this Solution of Nitre, two Drachms of Sal Armoniac; which wholly and easily dissolved in the said Solution; though it would not bear a grain more of Nitre. I then added a third Drachm of Sal Armoniac, after that a fourth, and a fifth; all which, within the space of half an hour, were perfectly dissolved in the said Solution, without any precipitation of the Nitre.

10. §. In the making of this Experiment, two things, to render it infallacious, are to be noted. That the said Salts were not dissolved by the help of Fire, but only by a strong and continued Agitation. And that this was done upon a warm day: which I mention, because that even the changes of the weather will somewhat alter the Solubility of the Salts.

11. §. Having made the Experiment upon two Salts, I proceeded to repeat it upon three. And first I dissolved as much common Salt in ℥ij of Water, as that quantity would bear. Then having separated the subsiding portion; I put to the Solution, no less than five Drachms of Nitre, which by a continued Agitation, was wholly dissolved therein, neither the Nitre nor the common Salt being in the least precipitated. Then adding a Scruple more, it would not dissolve, but subsided. This second subsiding portion, I again separated; and then put to this Superimpregnation, near ʒj of Sal Armoniac, which was also dissolved as the former. And if as many more Salts had been added, ’tis probable that the same Water would have born some quantity of them all.

12. §. From this Experiment, it is a Conclusion demonstrated, That not only the visible Crystals, but the very Atomes of every Salt, at least those Particles which are ultimately dissolved in Water, have a different Figure one from another. Because that if they were all of one Figure; there would be no Superimpregnation, but the Pores of the same Water, would imbibe as much of one Salt, as answers to the total of two more Salts imbibed: that is to say, it would as well imbibe two Ounces of common Salt, as one Ounce of common Salt and another of Nitre: which yet is contrary to the Experiment. And it is the same thing, whether we suppose the Pores of Water to be also different, or not. Because, that if the Figure of all the said Atomes be the same; then their respect to the Pores of the Water must be the same, how different so ever those Pores be: which is also contrary to the Experiment. Besides it is a great presumption, to say, that the Pores, and therefore the Atomes of Water have different Figures; and yet not those of Salts.

13. §. From the same Experiment we may go upon good ground in Compounded Infusions; whether of Purgative, or other Materials. As not doubting, but that the same Menstruum may be highly impregnated with several Ingredients at once, whose operative parts may be therein copiously dissolved, without hindring either an Extraction, or causing a Precipitation one of an other.

14. §. The Second Enquiry is, With what difference this Superimpregnation of Water is made? which I find considerable. For a Solution of above five Drachms of Nitre may be superimpregnated with no less quantity of Sal Armoniac. And a Solution of five Drachms of common Salt, may be superimpregnated with as much Nitre. Yet neither a strong Solution (as of five Drachms) of common Salt, will bear above two Scruples of Sal Armoniac: nor will a strong Solution (as of five Drachms) of Sal Armoniac, bear above a Drachm of common Salt: for if above the said quantities of either of them be mixed together: they are both copiously and forthwith precipitated to the bottome of the Glass.

15. §. Whence, notwithstanding the former Experiment, yet are we admonished, not to infuse all manner of Ingredients in any proportion. Because though some do not, yet others will precipitate one another.

16. §. The Third Enquiry was this, Whether the Solution of a smaller quantity of several Salts, doth consist with the non-increase of the Bulk of the Water? For this I took a Bolthead with a slender Neck, conteining about a pint and a quarter of Water; and dissolved therein about ℥jß of Nitre. And marking the place to which the Water ascended in the Neck of the Bolthead: I then dissolved in the same Water about a Drachm of Sal Gemmæ: which little quantity, raised the Water above half an Inch higher then it was before. The like I observed in the addition of Nitre to a Solution of Sal Armoniac. So that to suppose the variation of the Salt doth prevent the increase of the Bulk of the Water, is a manifest Error.

17. §. From the same Experiment it also appears, That the ascent of the Water upon a Superimpregnation, is the same, by whatsoever Salt the first Impregnation be made. For instance, Let a Solution of Nitre ascend in the Neck of the Bolthead, suppose, to 10 Inches, then add ½ an Ounce more of Nitre, so as to raise the Water, suppose, 12 Inches or more, or less, according to the Bore of the Neck. In like manner, let a Solution of Sal Armoniac reach to ten Inches: then add again half an Ounce of Nitre; and it will reach just 12 Inches, or more or less, as before.

18. §. The Fourth Enquiry is, What quantity of the several kinds of Salt, may be dissolved severally in the same quantity of Water: that is to say, by agitation alone, without the help of fire, as I noted before. And upon tryal it appears, First, that two Ounces of Water will dissolve three Ounces of Loaf-Sugar and no more, except the Water be heated.

19. §. The same quantity of Water that is, two Ounces will dissolve above two Ounces of Salt of Tartar. I say above, for how much more, want of a greater quantity of Salt which I could confide in, made me that I could not finish the Experiment.

20. §. The same quantity, sc. two Ounces of Water, dissolveth an Ounce and a Drachm of Green Vitriol.

21. §. The like quantity dissolveth six Drachms and a Scruple or above ¾ of an Ounce of common Salt.

22. §. Of Nitre, Five Drachms two Scruples and an half.

23. §. Of Sal Armoniac, five Drachms and two Scruples.

24. §. Of Alum, not above two Drachms and a Scruple.

25. §. And of Borax, not above a Drachm and half a Scruple.

26. §. Of these note, That although Common Salt be very dissoluble, and will presently catch the moysture of the Aer: yet a much greater quantity not only of Salt of Tartar, but even of Loaf Sugar, and of Green Vitriol it self, may be dissolved in Water than of Common Salt.

27. §. Again, as the great Solubility of some, so the less Solubility of other Salts is also observable, as of Alum, and Borax. For the same quantity of Water will dissolve near four times as much of Green Vitriol, as it will of Alum. And of Sugar more than ten times as much. Of Green Vitriol near eight times as much as of Borax; and of Sugar, twenty times as much.

28. §. From this Experiment we are likewise cautioned, not only in the Infusion of several Ingredients together, but of any one singly; that such a proportion thereof to the Menstruum, be not exceeded. For all that is over and above what the Menstruum will bear, is either not extracted, or will be precipitated. As is evident not only in the Dissolution of the Salts above named, but in the Infusion of Plants themselves: as, for instance, of Senna; two Drachms whereof will impregnate four Ounces of Water as strongly, as if twice the quantity were infused; because the Water will bear no more of the Purgative Parts of that Body.

29. §. There is only one Salt more remaineth to be spoken of under this Experiment; and that is, the Crystals of Tartar. Whereof, it is somewhat strange to observe, that it will scarce at all dissolve in Water: not more, than even divers Resinous Gums, as Mastick, Tolu, Tacchamahacca, and some others will do. For if two Drachms, suppose of these Crystals, of Tartar (commonly sold for Cremor Tartari) be put to one Ounce of Water, scarce five Grains thereof will, by Agitation, be therein dissolved.

CHAP. II.

In which is shewed, that by the Solution of Salts in Water, some certain space, more or less, is gained. That the space is different according to the Nature of the Salt. And what the just space is, which is gained.

HE Fifth Enquiry is, Whether by dissolving of a Salt in Water, there be any space gained, or not. That is, whether the Bulk of the Water be greater before the Salt lying in it be fully dissolved, than afterwards. For tryal whereof, I took a Bolt-head with a slender Neck, holding somewhat more than a pint; and filling it up to a certain place in the Neck; I then put in an Ounce or two of Salt. And observing the hight of the Water, both before it was dissolved, and afterwards; It plainly appeared, that there was some, and that a considerable space, gained by the Dissolution; the Water thereby sinking several Inches below the place, where it stood after the Salt was first put into it.

2. §. From this Experiment it is plain, that there are Vacuities in Water. That is to say, that all the parts of Water are not contiguous, but that either betwixt, or in the Atomes of the Water themselves, there are certain Pores, either absolutely void, or at least filled up with another more subtile body which is easily excluded by the particles of Salt: by possessing the room of which the above said space is gained.

3. §. The Sixth Enquiry is, Whether the space be equally gained, by an equal encrease of the same Salt.

4. §. For this I made two tryals; the first was this. Two half Ounces of Salt Armoniac, being successively dissolved in the same Water; both of them raised up the Water in the Neck of the Bolt-head, equally; the first 3 Inches ⅝, and so the second.

5. §. The other was this. Four half Ounces of Nitre, being successively dissolved in the same Water, they all of them raised up the Water in the Neck of the Bolt-head, equally; the first a little above two Inches, and the 2ᵈ, 3ᵈ, and 4ᵗʰ, just as much.

6. §. The Seventh Enquiry is, Whether upon the Dissolution of several kinds of Salts, be gained so many several quantities of space. For this I made tryal upon Eleven several Salts, sc. Salt of Tartar, Common Salt, Sal Gemmeus, Roman Vitriol, Nitre, White Vitriol, Green Vitriol, Alum, Borax, Loaf-Sugar, and Sal Armoniac; of all which, I dissolved an equal quantity sc. two Ounces, in an equal quantity of Water, severally; that is, taking fresh Water for every Solution. The success was, That the Sal Armoniac raised the Water 15 Inches. The Loaf-Sugar, 13 Inches and ⅜ᵗʰˢ· The Borax, a Foot. The Alum 11 Inches, and ⅝ᵗʰˢ. Green Vitriol, 9 Inches and ⅝ᵗʰˢ· White Vitriol, 9 Inches and ⅛ᵗʰ. Nitre, 8 Inches, and ⅜ᵗʰˢ· Roman Vitriol, 7 Inches and ⅝ᵗʰˢ· Sal Gemmæ, 6 Inches, and ⅝ᵗʰˢ· Common Salt, 6 Inches and ⅜ᵗʰˢ· Salt of Tartar, not above 4 Inches and ⅛ᵗʰ. All which differences are plain, and most of them very remarquable: Two Ounces of Sal Armoniac raising the Water near four times as high, as the same quantity of Salt of Tartar.

7. §. From this and the fourth Experiment, compared, it also appears, That the several spaces gained by the several Salts, though sometimes they do, yet do not always answer to the Solubility of the said Salts. As to give some Instances; Loaf-Sugar is the most dissoluble of any other Salt; yet it gaineth less space than all the rest, save only Sal Armoniac. So Green Vitriol is more dissoluble then either Nitre or Common Salt; yet gaineth less space than either, especially than the latter. And Sal Armoniac, which is more dissoluble than Alum or Borax, yet gaineth less space than either of them. The Cause whereof is not easily assigned.

8. §. Note also, that by the same Experiment, as well as by the Taste and other Circumstances, it is plain, That Sal Gemmæ is nothing else but Common Salt, coagulated or Crystalliz’d under Ground.

9. §. Again, as the Fifth Experiment sheweth, That there are Vacuities in Water: so doth this Last, that those Vacuities, are of differing kinds. Because, otherwise, it should seem, That the Bulk of the Water would increase, more or less, according to the Solubilitie of every Salt, and not be alternately differenced as it is; Some Salts, more dissoluble, increasing the Bulk of the Water less, and others less dissoluble, increasing it more. I say, that this difference dependeth not only upon the different Figures of the Atomes of Salt; because then every Salt which is more dissoluble, would (quantity for quantity) take up less room in the Water: which is contrary to the Experiment.

10. §. From the same Experiment, howsoever paradoxical it may seem, yet is it also manifest, That although Water be a Fluid, yet the Particles thereof are hard and consistent, and unalterable in their Figure. Otherwise it is plain, That all manner of Salts would be dissolved in the same manner, and take up the same room in the Water. For let the Figures of the Salts be never so various, yet if the Particles of Water were themselves Fluid or Inconsistent and Alterable, they would always so conforme to those Figures, as to fill up all Vacuities; and so upon the Solution of several Salts, if of equal quantity, the Water would still retein an equal Bulk. As suppose an Ounce of Iron were drawn into Wyer, another beaten into Plates, a third made into Hooks, a fourth into Needles, a fifth into Nails; every one of these five Ounces, being put severally into Water will encrease its Bulk equally. I conclude therefore, That the Atomes of Water are hard and unalterable.

11. §. The Eighth Enquiry was this, What that just space might be, which any Salt gaineth upon Dissolution, with respect to its own Bulk, or the Bulk of the Water? For the making of this Experiment, Water will not serve, nor yet Spirit of Wine; because they both of them dissolve more or less of those Salts which are put into them; whereby the observation of the true Bulk of the Salt, and consequently of the just space it gaineth by Dissolution is lost. I took therefore Oyl of Turpentine, and pouring it into a Bolt-head, marked the place of its ascent in the Neck. Then pouring likewise into it two Ounces of Common Salt, I marked the second ascent of the Oyl; and found it to be 10 Inches and 6 eighths. Repeating the Experiment in like manner with two Ounces of Nitre, I found the ascent of the Oyl to be 11 Inches and ⅛ᵗʰ. Repeating it again with two Ounces of Alum, the ascent of the Oyl was 13 Inches and 2/8ᵗʰˢ· And making it once more with Sal Armoniac, the Oyl ascended to 15 Inches: the said several ascents of the Oyl being the true spaces which the Four abovesaid Salts take. From which, the space which the same Salts take up upon Dissolution, being deducted; the remainder is the space gained by that Dissolution. And so it appears, first, that Sal Armoniac gaineth nothing; being the only Salt of all I have tryed, which causeth the equal ascent both of the Water and the Oyl sc. just 15 Inches in both. Alum causeth the ascent of the Oyl to 13-2/8ᵗʰˢ, of the Water, to 11 Inches and ⅝ᵗʰˢ: So that it gains about 1 Inch and ½ out of 13. Nitre causeth the ascent of the Oyl, to 11 Inches and ⅛ᵗʰ; of the Water, to 8 Inches and ⅜ᵗʰˢ· So that Nitre by Dissolution gets almost the space of 3 Inches in 11. Common Salt causeth the ascent of the Oyl, to 10 Inches and 6/8ᵗʰˢ; of the Water, 6 Inches and ⅜ᵗʰˢ· So that Common Salt gains by Dissolution 4 Inches in 10, which is very considerable.

12. §. By this way the Specifick Gravity of all kinds of Salts may be easily taken, and the difference betwixt them is somewhat surprizing. For it appears by the Ascent of the Oyl, that Nitre, quantity for quantity, is about a 22ᵗʰ part lighter than Common Salt. Alum about a 6ᵗʰ part lighter. And Salt Armoniac, almost a 4ᵗʰ part lighter than Common Salt. The like estimate may be made of the Gravity of all other Salts.

13. §. By the same Experiment it also appears, That according to the Specifick Gravity of Salts they are many times at least more or less Volatile; as in the four last Salts is plain. For Common Salt which of all the four is the most fixed, is also the heavyest. Nitre which is somewhat less fixed is somewhat lighter. But Alum which is still less fixed is much lighter. And Sal Armoniac which is wholly Volatile, is the lightest of all the Salts above mentioned.

CHAP. III.

Wherein, from the Experiments in the foregoing Chapter, is shewed, the Cause of the Motion of the Mercury in the BAROMETER.

OR the doing of this, it will first be acknowledg’d, That not only several sorts of Sulphur, but also of Volatile Salts, are continually sublimed from most Bodies into the Aer. So Lightning, from the celerity of the ascension, appears to be made of a Meteor, which is Nitro-Sulphureous. Snow dependeth upon a Mixture of Nitrous, and other Salts; as is evident, from the regularly and differently Figur’d Parts, which compose the whole Body of a Snowy Cloud, before it clusters into Flakes. And one reason, why Rain is the best Water for any Soyl, is because it is impregnated with divers Volatile and Fruitful Salts. And so from other Meteors.

2. §. And next, that these Salts, are not always in the same Quantity, Proportion, and State, in the Aer: but that sometimes they are more copious; at others, less: sometimes, one more copious, than an other: sometimes, more plentifully dissolved; at others, more sparingly: and that, either as they are more or less pure and dissoluble; or according to the quantity of the Vaporous Parts in the Aer, in which they are incorporated or dissolved.

3. §. Thus much being granted, from the Experiments in the foregoing Chapter compared together, we may resolve our selves about some Phænomena in the Barometre. Which seems to vary, not so much with the meer Weight of the Aer, which hitherto hath been supposed: as by the different pressure it makes, in being crowded more at one time, than at another. That is, according as certain Nitrous, or other Saline Bodies, take up less Space in the Aer, when dissolved in the Watery Parts therein, than while they are undissolved.

4. §. And therefore it is especially to be observed, That as the Mercury commonly riseth in the Cylinder for some days, but always for some time, before the change of the Weather, whether for Snow or Rain: So, that then it presently falleth again, even before the Snow or Rain falls. Whereas, if the Weight of the Aer, were the only, or the chief Cause of the ascent of the Mercury; than as it riseth all the while the Weather is gathering, so it would keep its standing or heighth, until the Weather breaks and falleth down: which yet it never doth, but always falls before it; sometimes no less than a whole day. The Cause whereof is, in that all the while the Mercury riseth in the Cylinder, the Aer is crowded with more and more Saline Parts, which by the Winds, or otherwise, are carryed into it; and so causeth it to press upon the Mercury in the Box: but after that in some time the Salts are dissolved or incorporated in the Aqueous Parts of the Aer, as in Rain or Snow; so soon as that is done, there is some Space gaind; and so, before any Weather falleth, the Aer is less crowded, and presseth less upon the Mercury in the Box, which gives way to its descent in the Cylinder.

5. §. From hence also it is, that the Mercury riseth higher with Cold Winds, than it doth with those which are Warme. Both because that in cold Winds there is the greatest quantity of Nitre: and that the coldest Winds, are usually the dryest. So that the Nitre wanting Moysture fully to dissolve it; it takes up so much the greater space, and so causeth a greater pressure in the Aer, as hath been said.

6. §. Lastly, For the same reason it comes to pass, that the Mercury first riseth higher, and then falleth lower before Snow, than it doth before Rain. Because that for the production of Snow, the Aer is crowded with a greater quantity of Nitre, or some other like Salts; which before they are dissolved, take up so much the more space; and afterwards so much the less, even before the Snow falls: as hath been proved.

FINIS.