SCHEELE 141 



had carried out since early youth, simply in order to see their 

 results, which he then always remembered accurately, had 

 enabled him to collect a store of knowledge and observations 

 of nature, such as none of his trained contemporaries pos- 

 sessed. And since he did not work according to precon- 

 ceived principles, he saw a great deal and was able to discover 

 a great deal that a systematically trained person would have 

 regarded as impossible, because it conflicted with his prin- 

 ciples. 



Scheele's discovery of 'fire-air' - oxygen as we call it to- 

 day, - links up with the fact already known to Leonardo and 

 Guericke, that ordinary air consists of two components, one 

 of which supports combustion and breathing (oxygen), 

 while the other is incapable of doing so (nitrogen). Scheele 

 was successful in separately preparing the first of these. He 

 obtained it from saltpetre, from oxide of mercury, from man- 

 ganese dioxide (pyrolusite), and other substances, by heating 

 them. In this experiment, as in other preparations of gases, 

 he tied to the neck of the retort which was inserted in the 

 fire, a pig's bladder previously pressed flat, and this then filled 

 with the gas developed. Only when he wished to examine 

 the gas more carefully, did he allow it to rise up under water 

 into a glass vessel. In the latter he was then able to observe 

 the characteristic property of the new kind of gas, the sur- 

 prisingly brilliant combustion in it of carbon, sulphur, and 

 phosphorus. The burning phosphorus consumed all the 

 'fire-air,' so that when the experiment was undertaken in 

 a closed vessel, a vacuum remained, whereby a thin-walled 

 vessel was even crushed by the external pressure of the air. 

 Phosphorus, and also a solution of liver of sulphur, which 

 likewise absorbed oxygen completely, gave him the means of 

 determining the amount of oxygen contained in the atmo- 

 sphere. He also found that nitrogen has a less specific 

 gravity than oxygen, and that the latter is more soluble in 

 water than the former, which must be advantageous for the 



