A history of chemistry from earliest times to the present day : being also an introduction to the study of the science / by Ernst von Meyer ; translated with the author's sanction by George M'Gowan.

Date:
1891
Catalogue details

Licence: Public Domain Mark

Credit: A history of chemistry from earliest times to the present day : being also an introduction to the study of the science / by Ernst von Meyer ; translated with the author's sanction by George M'Gowan. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    nesia wliich corresponded to a definite amount of magnesia alba, in order^to prove the constant proportion of fixed air in the latter ? Mention must also be made here of the deter- mination of the weights in cases of metallic precipitates by Bergman and others. Bergman was the first to proceed on the principle that an element should not be itself isolated and estimated according to its own weight, but separated in the most convenient form as an insoluble precipitate, e.g. lime earth as oxalate of lime, and sulphuric acid as sulphate of baryta. In pneumatic chemistry, too, the necessity became strongly felt of being able to detect different gases in presence of one another by means of reagents, and to estimate their relative volumes, i.e. estimate them quan- titatively. For this purpose special absorptives were used, by the action of which the differences in the gases had first been noticed. Thus caustic potash was found to be suitable for the absorption of carbonic acid, and saltpetre gas (nitric oxide), hydrate of protoxide of iron, moist sulphuret of iron, or phosphorus, for the absorption of oxygen. Of course the results of such quantitative analysis were very inexact.^ Cavendish succeeded in making a very accurate determina- tion of the oxygen in air by the method suggested by Volta, viz. by exploding with hydrogen. Uulike previous experi- menters, he found the composition of the air constant, the oxygen amounting on the average to 20-85 per cent/the mean, as determined at the present day, is 20-9 per cent. As the foregoing short account shows, a great deal of preparatory work, which chiefly required perfecting in the quantitative direction, stood ready to hand at the period which began with Lavoisier. The most important features and principles of chemical analysis were contained in those preparatory researches, and only waited for development. 1 Priestley aud Scheele found that the proportion of oxygen in air varied between 18 and 25 per cent. The term eudiometry [emo,, fine (applied to weather), and ^Tpo,>, a measure] came into use then because it was supposed tliat the punty of the air was arrived at by the determination of its oxygen • and It has continued to be employed in gas analysis in spite of its inaptness. '