HISTORY OF CHEMISTRY: Torbern Bergman (1735-84). Etienne François Geoffroy (1672-1741). Carl Friedrich Wenzel (1740-1793). Jeremias Benjamin Richter (1762-1807).
The advance made during the last part of the 18th century in analytical chemistry is attributable in great measure to the labours of Torbern Bergman of Upsala (1735-1784), who derived systematic methods of examining compounds by the wet way, and by means of the blow-pipe, and first rendered it possible to analyze minerals insoluble in acids by fusing them with an alkali or alkaline carbonate. In 1718 E. F. Geoffroy had published tables in which he exhibited the reciprocal chemical affinities of various substances, and these tables had been improved upon by Gellert in his Metallurgic Chemistry, 1751, and by Limbourg, 1761. Bergman, in 1775, gave in a dissertation on elective attractions, as he named affinity, an arrangement in 59 columns of all the chemical substances known at the time, in which was shown the order of their decomposition when in solution, and when exposed to a strong heat. The nature of the compounds formed by the mixture of reagents depended, in Bergmans estimation, on the sum of their attractions. Bergman contributed also in some measure to the determination of the constitution of neutral salts a subject treated of by Homberg in 1699, and, after Bergman and Kirwan, investigated by Wenzel in his Vorlesungen über die chemische Verwandtschaft der Körper, published in 1777. From Wenzels observations the idea of equivalency took its rise. He showed that the products of the mutual decomposition of two neutral salts were themselves neutral, or, in other words, that the same weight of base satisfies definite quantities of two different acids, Thus, according to his experiments, 123 parts of lime and 222 of potash must be considered equivalent to each other, being both competent to neutralize 181·5 parts of sulphuric, or 240 parts of nitric acid.
In England, ten years previously to the publication of Wenzel's treatise, Cavendish described certain quantities of fixed alkali and marble as "equivalent;" and in 1788 he stated that a quantity of oil of vitriol sufficient to produce 100 parts of plumbum ponderosum with sugar of lead would dissolve 33 of marble, since he found by experiment that so much oil of vitriol would saturate as much fixed alkali as a quantity of nitrous acid sufficient to dissolve 33 of marble. -- (Phil. Trans., 1767, p. 102; 1788, p. 178.)
In 1792, J. B. Richter (1762-1807) published a work on Stöchiometrie, or the Art of Measuring Chemical Elements, in which he gave in two series of tables the weights of different bodies which neutralized 1000 parts of various acids, and the weights of acids that similarly corresponded to 100 parts in the case of the bases, and pointed out the proportionality that existed between the weights of the bases, as also of the acids, in each series . there was, he remarked, a constant ratio between the quantity of an acid and the quantity of oxygen in the weights of the bases needed for its complete saturation, -- a fact afterwards restated by Berzelius, who showed that a simple and uniform relation was observable between the amounts of oxygen in the acid and basic portions of salts of the same class.
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