The fundamental conception that underlay all Berthelot's chemical work was that all chemical phenomena depend on the action of physical forces which can be determined and measured. When he began his active career it was generally believed that, although some instances of the synthetical production of organic substances had been observed, on the whole organic chemistry must remain an analytical science and could not become a constructive one, because the formation of the substances with which it deals required the intervention of vital activity in some shape. To this attitude he offered uncompromising opposition, and by the synthetical production of numerous hydrocarbons, natural fats, sugars and other bodies he proved that organic compounds can be formed by ordinary methods of chemical manipulation and obey the same laws as inorganic substances, thus exhibiting the "creative character in virtue of which chemistry actually realizes the abstract conceptions of its theories and classifications--a prerogative so far possessed neither by the natural nor by the historical sciences." His investigations on the synthesis of organic compounds were published in numerous papers and books, including _Chimie organique fondée sur la synthèse_ (1860) and _Les Carbures d'hydrogéne_ (1901). Again he held that chemical phenomena are not governed by any peculiar laws special to themselves, but are explicable in terms of the general laws of mechanics that are in operation throughout the universe; and this view he developed, with the aid of thousands of experiments, in his _Mécanique chimique_ (1878) and his _Thermochimie_ (1897). This branch of study naturally conducted him to the investigation of explosives, and on the theoretical side led to the results published in his work _Sur la force de la poudre et des matières explosives_ (1872), while on the practical side it enabled him to render important services to his country as president of the scientific defence committee during the siege of Paris in 1870-71 and subsequently as chief of the French explosives committee. In the later years of his life he turned to the study of the earlier phases of the science which he did so much to advance, and students of chemical history are greatly indebted to him for his book on _Les Origines de l'alchimie_ (1885) and his _Introduction à l'étude de la chimie des anciens et du moyen âge_ (1889), as well as for publishing translations of various old Greek, Syriac and Arabic treatises on alchemy and chemistry (_Collection des anciens alchimistes grecs_, 1887-1888, and _La Chimie au moyen âge_, 1893). He was also the author of _Science et philosophie_ (1886), which contains a well-known letter to Renan on "La Science idéale et la science positive," of _La Révolution chimique, Lavoisier_ (1890), of _Science et morale_ (1897), and of numerous articles in _La Grande Encyclopédie_, which he helped to establish.