The chemical constitution of alcohol was speculated upon rather wildly by the chemists who experimented on it before Lavoisier. It was held to be a combination of phlogiston with water, but the phlogiston-philosophers disagreed on the question whether it contained an oil. Stahl, however, later supported by Macquer, found that an oil was actually separated from it if mixed with water and allowed to evaporate slowly in the open air, after treating it with an acid. Lavoisier, in 1781, carefully analysed spirit of wine and found that 1 lb. yielded 4 oz. 4 drms. 37½ grains of carbon, 1 oz. 2 drms. 5½ grains of inflammable gas (hydrogen), and 10 oz. 1 drm. 29 grains of water. It was de Saussure who later, following Lavoisier’s methods of investigation, but with an absolute alcohol which had been recently produced by Lowitz, a Russian chemist, showed that oxygen was a constituent of alcohol. Berthelot succeeded in making alcohol synthetically in 1854. His process was to shake olefiant gas (C_{2}H_{4}) vigorously with sulphuric acid, dilute the mixture with eight to ten parts of water, and distil. Meldola, however (“The Chemical Synthesis of Vital Products,” 1904), insists that an English chemist, Henry Hennell, anticipated Berthelot in this discovery. ALUM. Alum is a substance which considerably mystified the ancient chemists, who knew the salt but did not understand its composition. Ancient writers like Pliny and Dioscorides were acquainted with a product which the former called alumen and which is evidently the same as had been described by Dioscorides under the name of Stypteria. Pliny says there were several varieties of this mineral used in dyeing, and it is clear from his account that his alumen was sometimes sulphate of iron and sometimes a mixture of sulphate of iron with an aluminous earth. It is the fact that where the various vitriols are found they are generally associated with aluminous earth. Alum as we know it was first prepared in the East and used for dyeing purposes. Alum works were in existence some time subsequent to the twelfth century at a place named Rocca in Syria, which may have been a town of that name on the Euphrates, or more probably was Edessa, which was originally known as Roccha. It has been supposed that it was the manufacture of alum at this place which bequeathed to us the name of Rock or Rocha alum, but the Historical English Dictionary says this derivation is “evidently unfounded.”