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 synthetic compounds come to be constructed. The theory was that the physiological action of sulphonal was due to, or connected with, its ethyl group. It was supposed, therefore, that by increasing the number of such groups in a molecule the hypnotic effect would be proportionately developed. It was believed that experiments on dogs supported this deduction; but it was not maintained in clinical experience.

Many of the popular synthetic remedies belong to the benzene series. Benzene is obtained from coal-tar, but, as shown by Berthelot, it is possible to prepare it by heating the gaseous hydrocarbon, acetylene, C2H2, in a closed vessel. By this means three molecules of acetylene are condensed into one, C6H6, which is benzene. Benzene acted upon by nitric acid yields nitrobenzene, and this by the action of nascent hydrogen is changed into aniline. Aniline may be regarded as ammonia, NH3, in which one hydrogen atom has been replaced by the phenyl group, C6H5, and, like ammonia, it combines with acids to form salts. Aniline acetate being formed, the elements of water being eliminated in the process, the product is acetanilide, or antifebrin. Acetanilide was first prepared by Gerhardt, in 1853, but its physiological action was only discovered by Cahn and Hepp in the 'eighties. By the substitution of an ethoxy-group for one of the hydrogen atoms of acetanilide, para-ethoxy-acetanilide, commonly called "phenacetin" is produced.