As to the question, What is alcohol ? there was more or less speculation during the seventeenth and eighteenth centuries, but it was not till towards the close of the latter period that much was definitely proved. Stahl (1660-1734) regarded alcohol as a very light, attenuated oil, united by an acid to a larger quantity of water than was present in ordinary oils. Kunckel, however (1630-1702), gives excellent reasons why it cannot be an oil. It mixes with water, does not dissolve sulphur, and does not form a soap with alkali.

Another view (Junker) was that alcohol consisted of phlogiston united simply with water, since it was found that only water was produced when alcohol was burnt. Boerhaave also (1757) found that the product of combustion was pure water. Nevertheless, the "oil" idea still had its partisans. Lemery1 considered alcohol as the oily part of wine, but rarefied by the acid salts of the wine. Macquer2 gives both views, but adopts that of pure phlogiston without oil. He correctly regards the oily residue, left when alcohol (of wine) evaporates, as an impurity of the alcohol.

1 Scarisbrick, loc. cit, p. 48.

In Fourcroy's Traite de Chimie (An 11 de la Republique) another question is raised. Does alcohol pre-exist in wine, or is it formed during the boiling when wine is distilled ? The author indicates that the former view was that held by the older chemists; the more modern savants considered that wine contained two "principles," respectively characterised by (i) much hydrogen, and (ii) very little carbon; and that during distillation of the wine these combined to form alcohol. In 1806, however, Fourcroy3 no longer supports either this opinion or the oil theory. He regards alcohol as a product of the fermentation of sugar, which has been reduced to a "simpler term."