SummaryIn the history of chemistry, the Danish chemist Julius Thomsen (1826–1909) is best known for his contributions to thermochemistry. Throughout his life, he was a pronounced atomist and a tireless advocate of neo-Proutian views as to the constitution of matter. On many occasions, especially in his later years, he engaged in speculations concerning the unity of matter and the complexity of atoms. In this engagement, Thomsen was alone in Danish chemistry, but his works were representative of a large number of (...) 19th-century chemists, particularly in England and Germany. Thomsen's ideas as to the constitution of matter, the periodic system and the noble gases, may be seen as typical of this vigorous trend in fin de siècle chemistry. (shrink)

The influential French chemist Marcelin Berthelot spoke against the use of Dalton's atomic theory and Avogadro's hypothesis in the second half of the nineteenth century. This paper argues that Berthelot conceded that atomism might be acceptable as a system of conventions, but he feared the power of such conventions in constructing a realistic picture of atoms which was not warranted empirically. Equally, Berthelot's anti-atomism was a last-ditch effort to assert the place of chemistry within the tradition of natural history and (...) to deny the possible reduction of chemical science to the laws of nineteenth-century physics. (shrink)