in THE DISCOVERY OF OXYGEN 43 



change a great many of the substances with which it unites 

 into the state of acid, or rather because it appears to be a 

 principle necessary to acidity" (Chemical Nomenclature, 

 p. 24 ; compare Works, II. 249, where the name " oxygen " 

 is first used ) This name has been retained to the present day 

 in spite of the discovery (see Chapter XII) of acids in which 

 no oxygen is present. The compounds in which oxygen 

 was present were described as OXIDES ; under this title were 

 included, not only the acid oxides of sulphur and phos- 

 phorus, but also the basic calces derived from the metals. 



By making use of the discovery of oxygen, Lavoisier 

 had been able to explain all the main facts on which the 

 phlogiston theory was based ; the phlogiston theory was 

 therefore no longer necessary, and gradually ceased to be 

 used. Lavoisier's theory was completed in the year 1777. 

 It won its first converts nearly ten years later, when it was 

 accepted by de Morveau, Fourcroy, and Berthollet. The 

 " System of Chemical Nomenclature " which they issued in 

 1787 was one of the first manifestoes of the new faith. 



Scheele's discovery of oxygen. The separation of the 

 gases of the atmosphere was accomplished independently 

 by the Swedish chemist Scheele in a research, "On Air 

 and Fire " (A. C. R. VIII), completed about the same time 

 as Priestley's work, but not published until 1777, and not 

 known either to Priestley or to Lavoisier at the time when 

 they were carrying out their experiments. 



Scheele's experiments led him to the belief that common 

 air consisted of two gases, one of which could be removed 

 by various substances. Thus when damp iron filings rusted 

 in air, in a tightly closed bottle which was afterwards opened 

 under water, about a quarter of the air was found to be 

 absorbed. Similar results were obtained when phosphorus 

 was burnt in a thin flask tightly corked, or when it was 

 simply allowed to stand for six weeks in a closed flask until 

 it ceased to glow. The part of the air remaining at the 



