34 Mr. William Henry’s Experiments on the 
absorption, seems to be connected with the proportion of com' 
mon air contained in the unabsorbed residuum ; for, besides the 
unavoidable contamination of the gas employed, with a minute 
portion of the air of the vessel used for its extrication, a small 
quantity will always be liberated from the water, whatever 
pains have been taken to deprive it of air, by previous long 
boiling, exposure under the air pump, or both in succession. 
That this is the true explanation, appears also, from the result 
of adding to the gas a proportion of common air. Thus, when, 
at the temperature of 55 0 , 20 measures of carbonic acid are 
agitated with 10 of water, at least 10 measures of gas are taken 
up; but, from a mixture of 20 measures of carbonic acid with 
10 of common air, 10 parts of water take only 6 of carbonic 
acid, or 4 less than in the former instance. 
An analogous fact was observed by Dr. Brownrigg,* who 
remarked that gas does not escape from the water which it 
impregnates, unless the water be in contact with air : for, when 
the Pouhon water was excluded from air, but, at the same time, 
liberty was given for its gas to arise into an empty bladder, the 
gas did not spontaneously separate from the water; but, on 
the contrary, remained united with it, when exposed to the 
greatest heat of our climate. When the impregnated water, he 
observes, is thus excluded from air, the gas will escape very 
slowly, at any temperature less than 110° of Fahrenheit, al- 
though such heat be sufficient for the distillation of water ; nor 
can it be wholly expelled by a heat of 160° or 170°, continued 
two hours. But it is well known, that water saturated with car- 
bonic acid gives up its gas rapidly, when freely exposed to the 
atmosphere. 
* See Dr. Brownrigg’s Paper on the Pouhon Water, Phil. Trans, Vol. LXIV. 
