123 



venal blood*. We infer, therefore, from these 

 facts, that atmospheric air is decomposed by being 

 placed in contact with venal blood, its oxygenous 

 portion being in part converted into carbonic acid, 

 and a quantity of its nitrogen being, in consequence, 

 left free. 



99. But, supposing the air to be thus decomposed by 

 the blood, it still remains a question, whether it has 

 been first attracted by that fluid, then decomposed, 

 and afterwards in part expelled ; or, whether the de- 

 composition has been effected without such previous 

 attraction and intermixture of air. The only evi- 

 dence of this supposed attraction seems to be the small 

 diminution of bulk which the air in all cases suf- 

 fers ; but this cannot be considered as a proof of the 

 attraction of the air ; for it is a necessary conse- 

 quence of that conversion of oxygen gas into carbo- 

 nic acid which has been shewn (11.) to take place 

 when these substances are brought into contact. Even 

 granting to the blood this power of attracting air, 

 or its oxygenous portion, it is not easy to conceive 

 why it should so readily lose it, and again give out 

 this air in the form of carbonic acid. No change 

 of quality in the blood, nor any variation of tempe- 

 rature, can have taken place sufficient to alter so ra- 

 pidly its affinity for these substances : and it cannot 

 proceed from a want of affinity between the blood 

 and the carbonic acid that is formed ; for that acid 

 suffers a greater diminution, either than oxygen gas 

 or atmospheric air, by being placed in contact with 



* Davy's Researches, p. 37.-". 



