76 PRIESTLEY. 



most important discovery, which he thus connected 

 with an erroneous theory, was made on the 1st of Au- 

 gust, 1774. He afterwards discovered that its absorp- 

 tion by the lungs in the process of respiration gives its 

 red colour to arterial blood, as it was proved to act 

 through the substance of thin bladder ; and he found 

 that when plants grow in close vessels, and restore the 

 purity of the air in which a candle has burnt or an 

 animal breathed, they do so by evolving this pure air. 

 The new nomenclature gave it the name of ' oxygen 

 gas,' from the belief then generally entertained that it 

 was the acidifying principle. Later experiments have 

 proved that there is at least one great exception to 

 this in chlorine, formerly called ' oxygenated muriatic 

 acid ;' but now found to be wholly without oxygen, 

 and yet to have all the properties of an acid. But, in- 

 deed, water itself, and the atmospheric air, having 

 neither of them the nature of acids, are both contrary 

 to the theory ; and the fixed alkalis 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 so bad as 

 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 discovered the 



