246 The Rise of the Modern [lect. 



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wh ' a metal had been calcined in so far that it had lost a 



o 

 ce. Quantity of its oxygen. 



,-xjavoisier went further than this, he saw that there was 

 an essential difference betwee ir in which a metal had been 

 calcined and air which had 1 ~en breathed. The latter con- 

 tained what the former did not, Black's fixed air, for it 

 precipitated lime water. Lavoisier, unlike Priestley, with no 

 veil before his eyes, saw no reason to doubt that this fixed air 

 came from the lungs ; and he recognized accordingly that in 

 respiration there were two factors, the disappearance of oxygen 

 and the appearance of fixed air. 



He took a measured quantity, 12 inches of vitiated air, of 

 air which had been breathed, and passed it over caustic alkali. 

 It was diminished in volume by £th, and the caustic alkali was 

 found to have lost its causticity, and when treated with acid to 

 give off fixed air. Lavoisier found that Black's fixed air could 

 be rr readily prepared by treating chalk with acids, and he 

 had *^ed that it gave an acid reaction; hence he pre- 



ferred to ^ it aeriform calcic acid. Hence he states the 

 conclusion to rived from the experiment just quoted in the 



following terms. " Air vitiated by breathing contains £th part 

 " of an aeriform acid like that which is obtained from chalk." 



After this aeriform acid has been removed the air becomes 

 exactly like the air in which a metal has been calcined, it is 

 an air which extinguishes flame and is unfit for being breathed. 

 This residual air since it would not support life Lavoisier 

 proposed to call azotic air or azote. When this azote was 

 mixed, to the extent of Jth its volume, with air eminently 

 respirable, dephlogisticated air (he did not as yet feel justified 

 in using largely his new term oxygine), it became exactly like 

 common air, the air of the atmosphere. 



He draws from his experiments the following physiological 

 conclusion : 



" Either the portion of the air eminently respirable con- 

 " tained in the air of the atmosphere is converted into aeriform 

 "calcic acid, or a change 's effected in the lung by which on 

 " the one hand the air emv - respirable is absorbed, and on 



"the other hand the lung su ;utes in its place in nearly 

 " equal volume a portion of aeriform calcic acid. I shewed 



