THE LIFE OF KARL WILHELM SCHEELE xxiii 



Quartz, Clay, Alum. The reader is referred to the essays. 

 Calculi. Scheele was the first to separate lime and uric 

 acid from urinary calculi. 



1777. The Treatise on Air and Fire not being included 

 amongst the present Essays, does not call for detailed comment; 

 suffice it to say that Scheele discovered independently that 

 air consists of two bodies, one of which supports combustion 

 and another which prevents combustion, and that he was not 

 only able to separate these two gases by chemical means, but 

 also to re-form them. 



Sulphuretted Hydrogen. During these experiments 

 Scheele discovered sulphuretted hydrogen. 



Light and Heat, their action on Silver. Scheele during the 

 course of these experiments was the first to explain the action 

 of light upon silver. 



1778. Calomel and Algaroth, new methods of making. 

 In this year Scheele described new methods of making calomel 

 and algaroth. These are instances in which his experiments 

 were devoted to improving the methods of making drugs, of 

 his adhering more strictly to his own branch of the profession. 



Arsenite of Copper Scheele' s Green. But what has rendered 

 Scheele's name immortal more than anything else is the green 

 pigment, the arsenite of copper, which he discovered in this 

 year, and recommended it as a useful pigment in oil and 

 water-colour painting. Unfortunately, it is highly poisonous 

 although its toxicological effects have without doubt been 

 exaggerated. But, be that as it may, there is no advantage 

 to be gained by its use, and, as a matter of fact, at the present 

 day it takes its place amongst the long list of obsolete pig- 

 ments, being of a dirty olive disagreeable ugly shade of green, 

 lacking lustre and brilliancy, and if any one were so misguided 

 as to have a preference for such a shade, there would be 

 no difficulty in producing it from less harmful ingredients. 



