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Universität Leipzig Frantisek Wald’s “Operational” Chemistry At the end of the 19th century it was generally accepted that only substances that displayed a constant elemental composition should be regarded as a chemical species. The validity of this norm, however, was not founded, neither empirically nor logically. One attempt to explain why only substances with constant composition should be regarded as chemical species was Avogadro’s atomic resp. molecular theory. The introduction of the atomic theory into chemistry although very successful in explaining a multitude of chemical phenomena and of great prognostic power, was regarded at the beginning of the 19th century by many chemists just as a convenient tool and not as an adequate and “true” description of the phenomena. It was not until the end of the century the “realistic” point of view gained rapidly influence among the chemists, being also enhanced by similar ideas in physics, so that at the dawn of the 20th century the microscopic existence of atoms and molecules was the predominant metaphysical dogma in the European scientific community. Nevertheless, a minority of dissidents still existed who tried to propose a way of explaining the validity of the “law” of constant proportions of chemical species without recourse to such “hypothetical” entities like atoms and molecules. To this minority belonged Franz, or as he preferred to be called, Frantisek Wald. He was born on January 9, 1861 at Brandýsek in Bohemia from parents of German origin. After high school he studied chemistry at the German College of Technology in Prague. He joined the “Prague-Iron-Plants” as laboratory chemist at the Kladno plant of the company and advanced in 1886 to the position of the chief chemist. Wald was also occupied also with theoretical research that was documented in a series of publications mainly in the Zeitschrift für Physikalische Chemie and in the Czech journal Chemické Listy. In 1908 Wald took an appointment as chair of theoretical and physical chemistry and metallurgy at the Czech Technical University in Prague where he remained until his retirement in 1928. He died on October 19, 1930 in the Moravian Vitkovice. Wald’s theoretical chemical work was pervaded with the idea that chemical transformations could be treated as phase transitions obeying Gibb’s law of phase transitions. He regarded the law of constant proportions as a norm stating that only those phases should be considered as chemical species in a genealogical taxonomy that display constant composition over a broad range of physical conditions. Chemical individual are thus not “natural entities”, but rather preparates that have to be produced by performing well defined chemical operations. The main target of the chemist during a chemical reaction is to create conditions that enable the emergence of new phases with constant composition. Unfortunately Wald’s ideas were met with scepticism or even vigorous disapproval by his fellow chemists, with few exceptions like Wilhelm Ostwald. ד"ר ליאו קורי ,
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