CHEMISTRY OF THE EIGHTEENTH CENTURY. 351 



natural history. His reputation soon spread over Europe, and he was 

 made a member of all the scientific societies. His teaching attracted 

 students of all nations to Upsal. Bergmann's chemical investigations 

 were conducted with something of the rigour of mathematical demon- 

 strations. His works are very numerous, and they include original 

 papers not only on chemistry and mineralogy, but also on geology, 

 astronomy, and physics. The chemical works of Bergmann, with which 

 we are here chiefly concerned, were first his study of the properties of 

 Black's "fixed air" (carbonic acid), to which he gave the name of aerial 

 acid, for he proved that this substance played the part of an acid. He 

 completed Black's researches by showing that the causticity of the 

 alkalies prepared with quicklime (p. 63) depends upon the fact of the 

 quicklime depriving the alkali (carbonated alkali i.e., potash, soda- 

 ash) of carbonic acid, and that these caustic alkalies return to their 

 original condition when exposed to the air, because they absorb car- 

 bonic acid from it. But there is a notable feature in Bergmann's re- 

 search, namely, the determination of the proportions in which " aerial 

 acid" (carbonic acid) enters into the composition of "aerated salts" 

 (carbonates). The process he used is one which is still resorted to in 

 the analysis of carbonates. He dissolved a weighed quantity of mild 

 alkali (carbonate) in water in a flask, corked it, and weighed the whole. 

 Another smaller flask containing some acid was also weighed. The 

 acid was then very gradually added to the alkali, with certain precau- 

 tions to avoid any loss by any liquid carried away during the efferves- 

 cence. The total loss of weight of the two flasks together would re- 

 present the weight of carbonic acid expelled. By evaporating the liquid 

 and heating the residue so as to expel the surplus acid, Bergmann was 

 able also to find the weight of the product, and thus infer the weight 

 of the air required to saturate the alkali. Here is a table of one of 

 his results, but we give the modern names of the substances instead of 

 those used by Bergmann : 



100 parts of caustic soda require for their saturation 

 177 parts of sulphuric acid, 

 135 ,, nitric acid, 

 125 ,, hydrochloric acid, 

 80 ,, carbonic acid. 



100 parts of caustic potash require 

 78 parts of sulphuric acid, 

 64 , , nitric acid, 

 51 ,, hydrochloric acid, 

 42 ,, carbonic acid. 



Bergmann also gave the first analysis of carbonates, such as those 

 of calcium, barium, and magnesium, and made several important ob- 

 servations on their properties. Bergmann had a just opinion of the 

 composition of the atmosphere, which he thus describes : " Common 

 air is a mixture of three elastic fluids ; that is to say, of free aerial acid 

 (carbonic acid), but in quantity so small that it does not perceptibly 



