It was Lavoisier's analysis of alcohol in 1781, supplemented by de Saussure's analyses (1807-1813), which settled the question of the composition of alcohol. Lavoisier, whose other researches had disposed of the phlogiston theory, found that 1 lb. of spirit of wine vielded on combustion: -

Onces.

Gros.

Grs.

Carbon ..........................................................

4

4

37 1/2

Inflammable gas (hydrogen) ......................

1

2

5 1/2

Water, ready formed ...................................

10

1

29

The analysis was made by burning alcohol in a bell-jar filled with oxygen and placed over mercury, and estimating the carbon dioxide formed and the quantity of oxygen consumed. Lavoisier regarded the results as indicating that alcohol was a compound of carbon and hydrogen united with ready-formed water. The figures indicate, of course, an aqueous alcohol. According to P. Guichard,4 if we leave aside the water and calculate the carbon and hydrogen percentages, the result is 51.85 per cent, of carbon and 1336 per cent, of hydrogen, as compared with the theoretical quantities 52.17 and 13.04 per cent, respectively.

Discussing the results in 1793, Lavoisier concluded that the carbon and hydrogen contained in alcohol are not present in the form of oil; they are combined with such a proportion of oxygen as makes them soluble in water.

A more definite proof that oxygen is a constituent of alcohol came later from de Saussure, who took up the study in 1807-1813. He made analyses by various methods, including Lavoisier's combustion process, decomposition in a eudiometer, and finally by a process of passing the alcohol through a tube heated to redness. Lowitz had meanwhile (1796) shown how a strong alcohol could be obtained by treatment of rectified spirit of wine with freshly-heated potassium carbonate, so that de Saussure could work with a much less aqueous product than was at Lavoisier's disposal. From the results obtained with his red-hot tube experiments, he deduced the composition of alcohol to be: -

1 Chimie, 1754. 2 Dict, de Chimie, 1779. 3 "Philosophic Chimique." 4 "Traite de Distillerie," Vol. III. The quantities expressed in modern figures are given as: Carbon, 149.5785 grams, Hydrogen, 38-5325 grams.

Carbon ... ... ... .........

57.57

per cent.

Oxygen ...........................

28.47

"

Hydrogen...............................

13.90

"

The analysis is notably less exact than Lavoisier's as regards carbon and hydrogen, but more complete in respect of oxygen. Subsequent analyses by Gay - Lussac, Dumas, and Boullay established the composition more precisely.