I have given this account of Mr. Geoffroy's analysis of Vinegar at length, only because it differs in several respects from that described in the process, which is Mr. Boerhaave's, as well as from those delivered by several other Authors, who make no mention either of the saline matter, which Mr. Geoffroy found on the residuum of Vinegar, after its first distillation in the balneum mariæ, or of the volatile urinous Spirit and Salt, which he obtained from that residuum.
These differences may arise either from the manner of distilling the Vinegar, or from Mr. Geoffroy's Vinegar having been concentrated by freezing, or rather from the quantity, and, above all, from the age of the Vinegar, examined by those different Chymists.
The distillation of Vinegar serves not only to separate its Acid from a considerable quantity of earth and oily parts, with which it is entangled, but also to dephlegmate and concentrate it. Yet Mr. Lemeri affirms, that Vinegar is not distilled with a view to dephlegmate it. He condemns the common method of throwing away the first runnings as useless phlegm, and saving only what comes off afterwards; having, he says, observed, that the phlegm of Vinegar cannot be abstracted, like that of many other acid liquors, and that what comes over first is almost as sharp as what rises afterwards, be the fire applied at first ever so small.
There is reason to think that Mr. Lemeri did not carefully enough examine the strength of his Spirit of Vinegar, at the different stages of his distillation: for Mr. Geoffroy, in the Memoir above cited, gives an account of a distillation of Vinegar, the product whereof he examined with care, having for that purpose divided it into five different portions: and his experiments put it beyond all doubt, that the first portions of Spirit of Vinegar are far from being so acid as the last. This Vinegar was so strong before distillation, that it required six grains of Salt of Tartar to absorb two drams of it. Two drams of the first portion of his Spirit were absorbed by three grains only of Salt of Tartar: the Acid of the second portion took five grains to absorb it. (Each experiment was made with two drams of Vinegar). The third portion was absorbed by ten grains; the fourth by thirteen, and the fifth took no less than nineteen: which proves that Vinegar, like most other Acids, may be concentrated by distilling off the most aqueous part, which is lighter than the Acid.
There are therefore two ways of concentrating Vinegar, and separating its most acid part, namely distillation and congelation. These two methods may be successively applied to the same Vinegar, and a very powerful Acid obtained by their concurrence. Mr. Geoffroy having exposed to the frost, on the 19th of January 1739, the last russet-coloured liquor, drawn from the residuum of distilled Vinegar, found it so concentrated thereby, that it required sixty grains of Salt of Tartar to absorb two drams of it.
[CHAP. VI.]
The Acid of Vinegar combined with different SUBSTANCES.