352 HISTORY OF SCIENCE. 



change the colour of blue litmus ; of an air (nitrogeti) which is unable 

 to maintain either combustion or the respiration of animals, which we 

 shall call vitiated air until we are better acquainted with its nature ; 

 lastly, of an air (oxygen) absolutely necessary to combustion and animal 

 life, which constitutes about a fourth part of common air, and which I 

 regard as pure air." In short, Bergmann may be considered to have 

 made a tolerably complete study of carbonic acid gas, excepting its 

 composition and its liquefaction by pressure. 



The methods of analysing minerals by solution, precipitation, filtra- 

 tion, dessiccation, etc., were first reduced to precise rules by Bergmann. 

 He accurately analysed cast iron, wrought iron, and steel, and showed 

 how the properties of these substances are affected by their composi- 

 tion. 



It is said that when Bergmann was once complimented on his many 

 brilliant discoveries, he observed that his greatest discovery was the 

 discovery of Scheele, which is thus related : Bergmann had received 

 some saltpetre from a druggist, and in making use of it found it libe- 

 rated red fumes. He attributed this to impurity in the salt, and accord- 

 ingly sent it back to the druggist by one of his pupils. The druggist's 

 assistant, however, explained how this was caused by a certain decom- 

 position of the saltpetre, which invariably took place under certain 

 circumstances. When this was reported to Bergmann, he hastened to 

 the shop, and to his surprise and pleasure discovered that the apron 

 of the druggist's assistant covered a profound and accomplished che- 

 mist of rare intelligence, who had already discovered a number of facts 

 new to the science. 



CHARLES WILLIAM SCHEELE (1742 1786) was born at Stralsund, 

 and at fourteen years of age was apprenticed to a druggist at Gothen- 

 burg, and he afterwards acted as assistant in various places before he 

 came to Upsal, where he became acquainted with Bergmann and 

 Linnaeus. Scheele's important researches soon made his name famous. 

 Several attractive invitations were made to him to quit his obscure 

 occupation as druggist. Thus, Frederick the Great wished him to 

 reside in Berlin. But to these offers he turned a deaf ear, and con- 

 tinued in his original vocation. His desires were moderate, and a 

 pharmaceutical business being vacant in Keeping, a small town in 

 Sweden, he entered upon it, and continued in that place for about nine 

 years, or until his death at only forty-four years of age. It was during 

 his residence here that Scheele published his most important researches 

 in a series of mcmoires printed by the Royal Society of Stockholm. 

 Scheele was , remarkable for a rigorous application of the methods of 

 experimental science, and he was careful always to verify his facts. 

 But when he attempted to explain these facts he plunged immediately 

 into the slough of speculation which was represented by the doctrine 

 of phlogiston, and all his scientific caution on other points did not 

 hinder him from believing he had proved that phlogiston really ex- 



