412 PRIESTLEY. 



are found to owe their alkaline state and lose their 

 metallic, like other oxides, by uniting with oxygen. 



Priestley is the undoubted discoverer of oxygen. He 

 was the first who communicated a knowledge of it to 

 Lavoisier, at Paris, soon after he had made the dis- 

 covery ; nor can anything be more disingenuous than 

 that celebrated person's afterwards affirming that he, 

 Priestley, and Scheele, had all discovered it " about 

 the same time." He never discovered it until Priestley 

 discovered it to him. Bergmann's suppressing in his 

 book all knowledge of the experiments of Black and 

 Cavendish, the former published twenty and the latter 

 eight years before, was bad enough, but not equal to 

 Lavoisier's positive assertion contrary to what must 

 have been his positive knowledge. 



This great discovery was far from being the last 

 of its justly celebrated author. He discovered the 

 gases of muriatic, of sulphuric, and of fluoric acids, 

 ammonial gas, and nitrous oxide gas. He also dis- 

 covered the combination which nitrous gas forms 

 suddenly with oxygen ; diminishing the volume of 

 both in proportion to that combination ; and he thus 

 invented the method of eudiometry, or the ascertain- 

 ment of the relative purity of different kinds of atmo- 

 spheric air. 



It must not be forgotten, in considering the great 

 merits of Priestley as an experimentalist, that he had 

 almost to create the apparatus by which his processes 

 were to be performed. He, for the most part, had to 

 construct his instruments with his own hands, or if 

 he employed others, he had to make unskilful work- 

 men form them under his own immediate direction. 



