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 final states of the changing system. (3) "The Law of Maximum Work," or "the theorem of the necessity of reactions": every chemical change accomplished without the aid of external energy tends to the formation of a body, or system of bodies, the production of which evolves the maximum amount of heat. This law of Berthelot is of considerable importance, as it will often enable the chemist to decide beforehand whether a contemplated reaction is or is not possible by direct means, and if, because accompanied by absorption of heat, not possible in the direct way, it may enable him to bring it about by making it one of a series of reactions, the total effect of which is an evolution of heat. &hellip; This law is the fundamental principle of Berthelot's thermo-chemistry: "The quantity of heat evolved in a reaction measures the sum of the physical and chemical changes which occur in that reaction"—"ce principe fournit la mesure des affinités chimiques."

Berthelot's agricultural station and laboratory were at Meudon, and here experiments on vegetable soils, the fixation of atmospheric nitrogen in soils by the agency of microbes, the action of electricity on the growth of plants, etc., were conducted. Berthelot states that twenty-five pounds of nitrogen per annum per acre might be fixed by bacteria.

Berthelot's work on the explosive wave, his classical experiments on the union of carbon and hydrogen, and