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 many of its derivations were formed by Berthelot. He also formed methane by passing the vapour of carbon disulphide and sulphuretted hydrogen over hot copper; and by the action of carbon monoxide on a hot solution of caustic potash, potassium formate was produced, the formate yielding formic acid on distillation with hydrochloric acid. He formed hydrocyanic acid by the action of the electric spark on a mixture of nitrogen and acetylene.

Such were a few of the numerous syntheses of Berthelot, or the building up of chemical compounds, many of which were only obtained through the instrumentality of life, either animal or vegetable.

His contributions to chemical literature range over practically every department of the science: philosophical, historical, physical, pure, and applied.

In 1864 Berthelot began his great work on thermo-chemistry, and in 1879 he published his Essai de Mécanique Chimique fondée sur la Thermo-chimie. Although Favre, Silbermann, Andrews, Hess, and Thomsen had previously worked on problems bearing on heat and chemical changes, Berthelot is generally looked upon as the founder of thermo-chemistry.

His laws are the following:—(1) The heat disengaged in any reaction is a measure of the chemical and physical work accomplished in the reaction. (2) The total thermal value of a reaction is dependent only on the initial and