10 BLACK. 



it " veritable air et meme tres pure." We have, how- 

 ever, seen that, in the following year (1777), M. Mor- 

 veau's ideas were perfectly distinct on the subject; for 

 he treats it as a new substance, wholly different from 

 atmospheric air. The slowness with which Black's 

 doctrine made its way in France may be presumed 

 from Morveau's remark on causticity, already cited, 

 and also from this, that the article on 'Magnesia,' 

 published in 1765, dogmatically asserts Black to be in 

 error when he describes Epsom salts as yielding that 

 earth, "because," says the author, "those salts are 

 purely Seidlitian," " entierement Seidlitiens" (vol. x. 

 p. 858). In fact, Epsom salts, magnesia, limestone, 

 and sea-water are the great sources from which all 

 magnesia is obtained. The first of these substances is 

 in truth only a ccmbination of magnesia with sulphuric 

 acid. 



The other discoveries to which Black's led were as 

 slowly disseminated as his own. Oxygen gas had been 

 discovered, in August, 1774, by Priestley, and soon 

 after by Scheele without any knowledge of Priestley's 

 previous discovery ; yet in 1777 Morveau, who wrote 

 the chemical articles in the ' Supplement,' never men- 

 tions that discovery, nor the almost equally important 

 discovery of Scheele, chlorine, made in 1774, nor that 

 of azote, discovered by Rutherford in 1772, nor hydro- 

 gen gas, the properties of which had been fully inves- 

 tigated by Cavendish as early as 1766. Lavoisier's 

 important doctrine, well entitled to be called a dis- 

 covery, of the true nature of combustion, had likewise 

 been published in 1774 in his ' Opuscules,' yet Mor- 

 veau doggedly adheres to his own absurd theory of 

 the air only being necessary to maintain those oscilla- 

 tions in which he holds combustion to consist ; and 

 finding that the increase of weight is always the result 

 of calcination as well as combustion, he satisfies him- 

 self with making a gratuitous addition to the hypo- 

 thesis of phlogiston, and supposes that this imaginary 



