Elements of the Theory and Practice of Chymistry, 5th ed.

by Pierre Joseph Macquer

The Oil with which the Volatile Salt is loaded, when but once distilled, is perceivable only by the yellow colour and weight it communicates thereto; because it is closely united therewith, and in a perfectly saponaceous state. This appears from the facility with which Volatile Salts, even the most oily, dissolve in water, without discovering in the solution any separation of the oily parts, and even without giving it a milky colour. But, in the second rectification, this Oil becomes very perceptible; for it then separates, in a great measure, from the Salt, and remains at the bottom of the cucurbit, floating on the phlegm, which is also separated from the Salt.

The Salt is then whiter, more volatile, and purer; yet it is still far from being brought to the utmost degree of purity, even by this second rectification. It requires a third, a fourth, and even many more rectifications, to purify it perfectly: every rectification separates from it some oily particles: and if you should resolve to go on rectifying till you can separate no more Oil, there is reason to think this Salt would be entirely decomposed; because there is necessarily a certain quantity of Oil in its composition, without which it would not be a Volatile Alkali. You must therefore desist from rectifying it any further, when you find it very white, and very light; and shut it up in bottles hermetically sealed.

It often happens that Volatile Salts, though of a beautiful white after rectification, grow yellow after being kept some time in close bottles. This is occasioned by the Oil they contain disengaging, and discovering itself by degrees. To remedy this inconvenience, Mr. Boerhaave proposes to mingle the Volatile Salt, which you intend to purify, with four times its weight of pulverized chalk, thoroughly dried, and even heated; to put the mixture into a glass alembic, and distil it with a gentle heat. By this means the Salt rises exceeding pure and very white; because the chalk absorbs most of its Oil, and frees it therefrom. He adds, that Volatile Salt thus purified may be kept a long time, and will retain all its whiteness.

If a Volatile Alkali thus purified be combined, to the point of saturation, with an Acid, such as the Marine Acid for instance; the result of this union, as we shall afterwards see, will be a Sal Ammoniac, from which the Volatile Alkali may be separated by the intervention of a Fixed Alkali. A Volatile Alkali that hath passed through all these trials will then be in the highest degree of purity that Chymistry can bring it to, and appears constantly the same, from whatever substance it was originally obtained: which proves that if Volatile Alkalis, extracted from different vegetable and animal substances, seem to differ from each other in some respects, this can arise only from the heterogeneous matters with which they are mixed; but that, at bottom, they are all constituted of one single principle, which is constantly the same, and exactly alike in them all.

It is of the last consequence, on all occasions where a Volatile Alkali is to be distilled in a concrete form, to make use of subliming vessels with very large necks, that it may have room enough to make its way to the receiver with ease; for otherwise it may choak up the passage, and burst the vessels.

PROCESS II.

Volatile Alkalis combined with Acids. Sundry Ammoniacal Salts. Sal Ammoniac.

On a Volatile Spirit or Salt pour gradually any Acid whatever. An effervescence will arise, and be more or less violent according to the nature of the Acid. Go on adding more Acid in the same manner, till no effervescence be thereby excited, or at least till it be very small. The liquor will now contain a semi-volatile Neutral Salt, called an Ammoniacal Salt; which may be obtained in a dry form by crystallizing as usual, or by subliming it in close vessels, after the superfluous moisture hath been drawn off.

OBSERVATIONS.

Volatile Alkalis have the same properties with Fixed Alkalis, fixity only excepted: so that a Volatile Alkali must produce an effervescence when mixed with Acids, and form therewith Neutral Salts, differing from each other in nothing but the nature of the Acid in their composition.