290 DR. DAVY'S ACCOUNT OP SOME EXPERIMENTS ON THE BLOOD. 



state of carbonate ; others that it is saturated with this gas, and in the state of bi- 

 carbonate. 



The subject, it must be confessed, is one of great difficulty, and very perplexing ; 

 partly from the nature of the blood, liable to great variations during life, and to rapid 

 change after death ; and partly also from the nature of the alkaline carbonates, hardly 

 less disposed to change than the blood itself, from variation of circumstances, and to 

 pass from one degree of combination into another. 



The bicarbonate of soda, I believe, like the bicarbonate of ammonia, can only exist 

 in perfection in the solid state. In dissolving, I find, when exposed to the atmosphere, 

 it gives off a part of its acid, and still more when it is agitated with common air, and 

 more still with hydrogen, and in a greater degree the higher the temperature. This 

 is not favourable to the idea that it exists in the blood, especially when it is consi- 

 dered that this fluid may be exposed to a temperature of 212° without disengaging 

 carbonic acid, of which I have had proof in several trials. 



Sulphuretted hydrogen does not expel carbonic acid from the alkalies in solution 

 in water. Bicarbonate of soda dissolved to saturation in distilled water absorbs, I 

 find, 143 per cent, of its volume of this gas ; whilst the serum of blood (it was Sheep's 

 that was tried) dissolved 207 per cent., arterial blood 235, and venous 290. This, 

 too, is unfavourable to the same idea ; as is also the large proportion of carbonic 

 acid which blood, it has been shown, is capable of absorbing. 



Supertartrate of potash occasions an effervescence, when mixed in substance with 

 a solution of the sesquicarbonate, but not of the carbonate of soda ; and the effect 

 is similar, whether the mixture be made over mercury, air excluded, or in an open 

 vessel exposed to the atmosphere. The supertartrate of potash also, I find, mixed 

 with blood and agitated with common air, acts as with the sesquicarbonate, and oc- 

 casions a disengagement of air, and both from arterial and venous blood, and from 

 serum ; and the air I have ascertained is carbonic acid. 



From these facts, may it not be inferred that the alkali in the blood, in its normal 

 or healthiest condition, is neither in the state of carbonate nor of bicarbonate, but of 

 sesquicarbonate ? The power of the blood to absorb carbonic acid and sulphuretted 

 hydrogen accords best with this view, and some other important properties of the 

 fluid are, I believe, in harmony with it. 



The sesquicarbonate, I may add, seems to be the state of rest of the alkali in com- 

 bination with carbonic acid, under ordinary circumstances of exposure to the atmo- 

 sphere. Thus the native compound is the sesquicarbonate, as is also, I believe, the 

 effloresced salt*. And I find that although a solution of the bicarbonate may be 

 brought by the air-pump to the state of sesquicarbonate, it cannot be reduced to 

 that of the carbonate : after it has ceased to give off any air in vacuo, it effervesces 



* On exposing carbonate of soda in excess to carbonic acid gas over mercury, the gas is rapidly absorbed 

 with the expulsion of part of the water of crystallization, so as to produce an appearance of deliquescence, 

 and the sesquicarbonate is formed. 



