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

by Pierre Joseph Macquer

Now all this is applicable to Fat Oils, when compared with light Essential Oils, in point of inflammability. If all these Oils were of the same nature, and differed from each other in weight and thickness only, the objection drawn from Fat Oils, which though thicker than Essential Oils do not take fire so easily, would be a very good one, and fact would be against our reasoning. But this is far from being the case: the properties, as well as the analysis, of Fat Oils shew their nature to be very different from that of Essential Oils; that there is more water in their composition; and that they are full of a mucilaginous or gummy principle, which must greatly obstruct their inflammability, and the action of Acids upon them.

None of the effects, therefore, that attend the firing of Oils with Acids, is repugnant to our way of accounting for the phenomenon, which is one of the most beautiful in all Natural Philosophy. To conclude this important subject, nothing now remains but to consider the effects produced by the Vitriolic Acid in these accensions.

This Acid, though of a stronger nature, and capable of being more highly concentrated than the Nitrous Acid, seems however less qualified to produce a flame with Oils. Indeed Mr. Homberg fired Oil of Turpentine by mixing it with Oil of Vitriol: but I do not know that the experiment hath succeeded with any other Chymist; on the contrary, most of those who have tried it affirm, that they never could fire any Oil with that Acid alone.

Oils are probably in the same case as metallic substances, with regard to these two Acids. We know that the Nitrous Acid dissolves those substances with vastly more activity and violence than the Vitriolic Acid exerts upon them; which may depend, either on the disposition and configuration of their parts, or on the portion of phlogiston which, according to the opinion of most Chymists, is united with the Nitrous Acid, is its peculiar characteristic, and the cause of the great vivacity with which it dissolves almost all matters that contain the phlogiston.

I say almost all matters that contain the phlogiston; because there are some substances that contain a great deal thereof, and yet are not at all acted on by the pure Nitrous Acid. These substances are matters perfectly charred: that is, such as are capable of enduring the greatest violence of fire in close vessels, without yielding a single atom of Oil; that burn almost quite away, yet only grow red hot without flaming; or at least produce but a very small, slight flame, from which it is impossible to obtain the least particle of soot or fuliginosity; in a word, that contain an inflammable matter, but such as is fit to be an ingredient in the composition of metallic substances, to which the peculiar title of the Phlogiston is appropriated.

I say, then, that if the Nitrous Acid be poured on a mere coal, perfectly charred, it is impossible for the Acid, be it ever so highly concentrated, to set the coal on fire, though heated before to the greatest degree that it can possibly admit of without kindling; and, which is still more remarkable, if a live coal be plunged into the most highly smoking Spirit of Nitre, it will be extinguished as if dipt in pure water.

But to return to the Vitriolic Acid: it is singular enough that this Acid, which attacks Oils with less activity, and for that reason seems less fit to set them on fire, than the Nitrous Acid, yet greatly promotes their accension, when mixed with that very Acid. This may be owing to its rendering the Oils with which it mixes heavier and thicker; or else, as Mr. Rouelle conjectures with great probability, being more concentrated than the Nitrous Acid, and having a greater affinity with water, it dephlegmates the other, and thereby increases its activity; or, lastly, this may arise from some other cause yet unknown to us, and perhaps from that by which the Acids of Nitre and of Sea-salt, which, when separate and perfectly pure, can neither of them dissolve Gold, are enabled, when combined together, to make a perfect solution of that metal.

PROCESS III.

To combine Essential Oils with Mineral Sulphur. Balsam of Sulphur. This Composition decompounded.

Put into a matrass one part of Flowers of Sulphur; pour on them six parts of the Essential Oil of Turpentine, for instance; set the matrass in a sand-bath, and heat it gradually till the Oil boil. The Sulphur, which at first lay at the bottom of the matrass, will begin to melt, and appear to dissolve in the Oil. When it hath boiled in this manner for about an hour, take the matrass from the fire, and let the liquor cool. A great deal of the Sulphur that was dissolved therein will separate from it as it cools, and fall to the bottom of the vessel in the form of needles, much like a Salt shooting in water.