Thirdly, some authors pretend that, by distilling the mixture under consideration, an oil is obtained greatly resembling that which, as we observed above, rises from spirit of wine combined with the vitriolic acid: others again deny this. For my part, I believe the thing depends on the different concentration of the spirit of nitre, as well as on the quality of the spirit of wine, which is sometimes more sometimes less oily.
Fourthly, the two liquors we are speaking of, being intimately mixed by distillation, form a liquor slightly acid, used in medicine, and known by the name of Sweet or Dulcified Spirit of Nitre: a very proper name, seeing the nitrous acid, by uniting with the spirit of wine, actually loses almost all its acidity and corrosive quality.
Fifthly and lastly, when the distillation is finished, there remains in the bottom of the vessel a thick blackish substance, nearly resembling that which is found after distilling oil of vitriol and spirit of wine.
Spirit of salt hath likewise been combined with spirit of wine; but it does not unite therewith so easily or so intimately as the two acids above-mentioned. To mix them thoroughly, the spirit of salt must be highly concentrated, and smoking, and moreover the assistance of the still must be called in. Some authors pretend that from this mixture also a small quantity of oil may be obtained; which probably happens when the liquors have the qualities above-specified. The marine acid likewise, by uniting with spirit of wine, loses most of its acidity; on which account it is in like manner called Sweet or Dulcified Spirit of Salt. A thick residuum is also found here after distillation.
[CHAP. XIV.]
Of the Acetous Fermentation.
Besides an ardent spirit, wine affords a great deal of water, oil, earth, and a sort of acid which shall be considered presently. When the spirituous part is separated from these other matters, they undergo no further change. But if all the constituent parts of wine remain combined together, then, after some time, shorter or longer as the degree of heat in which the wine stands is greater or less, the fermentation begins afresh, or rather arrives at its second stage. The liquor once more grows turbid, a new intestine motion arises, and, after some days, it is found changed into an acid; which, however, is very different from those hitherto treated of. The liquor then takes the name of Vinegar. The acetous fermentation differs from the spirituous, not only in its effect, but also in several of its concomitant circumstances. Moderate motion is of service to this, whereas it obstructs the spirituous; and it is attended with much more warmth than the spirituous. The vapours it produces are not noxious, like those of fermenting wine. Lastly, Vinegar deposites no tartar, even when the wine employed in this operation is quite new, and hath not had time to discharge its tartar: instead of tartar, Vinegar deposites a viscid matter which is very apt to putrify.
It must be observed, that wine is not the only substance that is susceptible of the acetous fermentation: for several vegetable and even animal matters, which are not subject to the spirituous fermentation, turn sour before they putrify. But as vinous liquors possess in a very eminent degree the property of being susceptible of the acetous fermentation, and likewise of producing the strongest acids that can result from such fermentation, their acid shall be more particularly considered in this place.