ix] Doctrines of Respiration. 247 



"during Easter 1775 that air eminently respirable could be 

 " entirely converted into aeriform calcic acid by the p f 



"charcoal, and in other memoirs I shewed the same 



"other means" (that is to say, he had proved that hu 



fixed air was a compound of carbon and oxygen). " This makes 

 " the former of the two views possible. On the other hand it 

 " is also possible that the air eminently respirable combines 

 " with the blood. We know that it is a property of the air 

 " eminently respirable to communicate a red colour to the 

 " bodies with which it combines, especially metallic substances, 

 " as, for example, mercury, lead, and iron. May we not conclude 

 "that the red colour of blood is due to a combination of the air 

 " eminently respirable, or more exactly, as I shall shew in a 

 "memoir shortly to appear, to the combination of the base of 

 " the air eminently respirable with an animal liquid, in the 

 " same way that the red colour of red mercury precipitate and 

 " nimium is due to a combination of the base of the same air 

 "with a metallic substance? For Priestley has sh ■■' hat 

 "blood becomes red when exposed to air eminent \ ole, 



"and dark when exposed to aeriform calcic aci3 in the latter 

 "case becoming red again when exposed o ,e more to air 

 " eminently respirable. 



" We may therefore regard as proved, 



" 1. Respiration affects only the air eminently respirable ; 

 " the rest of the atmosphere, the mephitic part," the part which 

 he later called azote, " remains unchanged. 



" 2. The calcination of metals in atmospheric air goes on 

 " until the air eminently respirable contained in the atmosphere 

 " is exhausted and combined with the metal, but will not go 

 " on afterwards. 



"3. Animals shut up in a confined atmosphere succumb, 

 " so soon as they have absorbed or converted into aeriform 

 "calcic acid the greater part of the respirable portion of the 

 "atmosphere, leaving a remainder. 



" 4. This remainder is the same in calcination and in respi- 



" ration, provided that in the latter^ case the aeriform calcic 



" acid be removed ; and in case is reconverted into 



- ■ u 

 "ordinary atmospheric air/ r r .mg to it air eminently 



" respirable. 



