The pre-history of cryoscopy: what was done before raoult?

Abstract

Recebido em 17/7/08; aceito em 10/2/09; publicado na web em 3/7/09Cryoscopy is considered one of the foundations of the modern theory of solutions and of physical chemistry. This paper shows in order the first regularities pointed out by several scientists on the subject, in the first chapter of its birth as a scientific discipline. The study is focused on the identification of the different steps that helped, first qualitatively and then quantitatively, to adjust the different classes of possible solutions, including those that formed hydrates, to a basic formulation that the French scientist François-Marie Raoult would later generalize in the law that bears his name.Keywords: cryoscopy; history; freezing point.The excessively brief style used by most textbooks to present the historical events associated with the emergence, development, and discussion of laws, theories and hypotheses related to scientific concepts, usually tends to create in the reader a distorted or incomplete version of the real facts. The history of cryoscopy's birth as a scientific discipline constitutes a good example of this situation.Cryoscopy is usually defined as the branch of science that studies the solutions founded on the determination of their corresponding freezing points. It allows, just like the other colligative properties, the determination of the molecular weight of a an unknown or unidentified substance based on the principle that the freezing point of a solution compared with that of the respective solvent varies according to the amount and nature of the solute dissolved in it. The origins of cryoscopy (from Greek roots, κρυος ice, and σκοπεω I examine) have been generally associated, in an almost exclusive way, with the name of the French professor of chemistry François-Marie Raoult (1830-1901. Through a very accurate and systematic experimental work on this subject, he was able to formulate a freezing point law that holds not only for water but also for other solvents, which include solutes of both, organic and inorganic nature. The very little cited information included in textbooks on physical chemistry about the different colligative properties seems to show that Raoult was gifted with the relevant information. According to that, it wouldn't be possible to know that the subsequent evolution of the subject was the result of many trials, successes, failures, approximations, and mistakes. Although it is true that he was responsible not only for the quantitative generalization of the connection between the lowering of freezing point of a solution and its corresponding concentration, but also for the proposal of the name for this branch of chemistry, the first observations about this subject go back to more than a century before Raoult's researches.The purpose of this article is show in order the first regularities pointed out by several scientists on the subject, which would later lead to the formulation of what could be considered one of the foundations of the modern theory of solutions and of physical chemistry. The spe...

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