A chemistry without hypothesis ? Maurice Delacre (1862-1938) and the history and philosophy of chemistry

Brigitte van Tiggelen

Mémosciences asbl, Louvain-la-neuve

At the end of scientific career devoted to organic chemistry, the Belgian chemist Maurice Delacre published a creed in positivist chemistry in 1934. This was his last contribution to the Bulletin de la Classe des Sciences of the Royal Belgian Academy of which he was a member, and also his last scientific paper for afterwards, he focused on his hobby : the influence of drawing in the painting of Van Dijck, Rubens and Michel-Angelo. Quelques considerations sur la chimie positiviste concludes on the conviction that chemistry can not be based on hypothesis, and should on the contrary be the paragon of scientific discipline since no other allows so clearly to draw a line between what is certain and what is doubtful, what is a fact and what is hypothetical. Maurice Delacre began his career in the Laboratory of organic chemistry of Louis Henry (1834-1913) at the Université catholique de Louvain. He recalls himself to have been educated as a chemist in the theories of Wurtz. But fifty years later, he comes to the conclusion that not only atomism, valency, and the periodic table are mere hypothesis and should only be considered as “thinking-tools” with caution. He also rejects structural and even linear formula. This leads him to develop a concept of “chemical individuality” : a chemical individual is no more defined by a specific and unique formula. These convictions grew out of his laboratory bench work, focusing on the gradual synthesis of the benzene chain, along which he studied thoroughly the structure of compounds like several pinacols, whose chemical behavior was unexplainable in terms of the organic chemical concepts of the time. Facing the fact, and letting go of the theory, Maurice Delacre turned to history and philosophy to make sense of what he perceived as an impasse in his field. He published his Histoire de la chimie published in 1920, which was later quoted by Helene Metzger as the perfect counter-example to her own approach to the history of chemistry. And three years later, in 1923, he published his Essai de philosophie chimique , published in 1923, in which he formalizes the teachings of his experimental work and criticizes the way theories of chemistry are introduced as the foundation of chemical education.