Technikatörténeti szemle 19. (1992)

KÖNYVISMERTETÉS - Papers of the First „MINERALKONTOR” International Conference on the History of Chemistry and Chemical Industry (Veszprém, 12-16 August, 1991)

attempts to determine the composition of a substance chemically go back to the 18th century. This was the time when the gas chemistry was being born and Lavoisier's theory of burning began producing hypotheses on the acid properties of oxygen and the oxygen structure of- acids. And although a new look at the processes of burning contributed to far-reaching transformations in theoretical chemistry, the experiments aimed at determining the composition of atmospheric air were of much greater importance for analytical researches. They were started in 1775 by the English naturalist Henry Cavendish. Similar researches were being done by other naturalists in the belief that the oxygen content in the atmosphere depends on the geographical situation and the climate. This assumption led to the formation of a new branch of chemistry — eudiometry, the name of which being derived from a measuring instrument, the eudiometer invented by A. Volta for the determination of gaseous substances. Eudiometry was discarded a few years later when it appeared that it was based on false premises, still the methods developed for gas mixtures did survive and find their application in pharmacy. The eudiometrical methods made determination of carbon dioxide, hydrogen sulfide, oxygen, hidrogen possible by making use of those substances' characteristic properties. For instance, the reagent used to identify carbon dioxide was lime water, gaseous hydrogen sulfide was detected by means of lead acetate or silver nitrate, oxygen used to be eliminated from a mixture through burning a piece of phosphorus, while hydrogen was bound quantitatively in the reaction of water synthesis carried out by using Volta's eudiometer or the Gay-Lussac eudiometer of platinum. The working out of analytical methods for gas mixtures contributed to the emergence of new branches in pharmaceutical sciences: balneochemistry and phytochemistry. Early in the 19th century, great significance used to be attributed to gas substances soluble in mineral waters, so an investigation of medicinal properties of mineral waters was started with heating a sample in a distillator and collecting the gases separated in this way into cylindri-form glass vessels placed over a mercurial gas washer. The gases were then identified and quantitatively determined. In later years, eudiometry was gradually replaced by the determination of gases in solution likewise other components of mineral waters. The first half of the 19th century was for balneology an epoch of research methods called ..balance analysis". Quantitative determination of contents was carried out via a precipitation process applied to the aqueous solution of a mixture of sedimentary compounds dissolving slowly in water, which were then obtained through a reaction with a substance selected properly for each compound and acting as a reagent. By the mass of sediments, making use of data on the percentage composition of obtained chemical combinations, the quantitative composition of the given sample was calculated. The methods used for determining gases proved essential for phytochemistry as well, because — through an analysis of the gas products of burning — they allowed to determine the stoichiometric composition of medicinal substances isolated from herbs. The gas products of burning vegetable stuffs had already been investigated by Lavoisier, who established that plants was made up only of a few chemical elements. As late as the end of the 18th century, investigation of the chemical compo-