1816.] ihe Absorption of Gases ly Water. 22) 
and vol. vii. p. 23.) My words are “ most liquids except.” 
Those expressions, are, I believe, not generally deemed synonymous. 
My experiments were much more numerous on water than on other 
liquids, and what I had more particularly in view was to show that 
any slight modification of water by acids, salts, &c., such as might 
naturally occur, was not sensibly distinguishable from pure water in 
regard to absorption. On concentrated liquid acids and saline 
solutions I had not made many experiments. A strong solution of 
common salt I found to absorb only one third of the volume of any 
gas that water did, and this was the reason of my saying “ most” 
instead of * all liquids except ;” but guarded as the expres- 
sion was, I am ready to allow that it was not sufficiently so. Saus- 
sure’s copious experiments on other liquids than water far surpass 
maine in number and variety, and will be found a valuable acqui- 
sition, if the accuracy of the less absorbable gases be equal to that 
of the more absorbable ones. 
If the influence of chemical affinity did not exist, the gases 
would be absorbed by all liquids in the same order, according to 
Saussure; and finding them not so, he concludes, that the absorp- 
tions are occasioned by aflinities. A better distinction in my opi- 
nion would be, that if a volume of any gas or mixture of gases is 
absorbed by water in proportion to the pressure of the incumbent 
gas, and the same volume is capable of being expelled again un- 
changed by the usual means of boiling, the air-pump, or agitation 
with any other gas, then the absorption is mechanical; but if a 
change in the quantity or quality of the gases expelled be observed, 
it must be ascribed to affinity: thus when nitrous gas or sulphu- 
reted hydrogen are pressed into pure water freed from all air, we 
can rarely if ever recover the same quantity again, the respective 
gases being in a short time partially decomposed. If it be said 
that solutions of ammonia, muriatic acid, &c. in water, must 
upon these grounds be considered as mechanical combinations; I 
grant they are combinations of a mixed nature, partly mechanical 
and partly chemical. ‘The immense condensation of volume of 
those gases by water cannot be accounted for on mechanical prin- 
ciples alone; the water must have an affinity for the bases of these 
gases, or for their caloric, or both, and besides the quantity is not 
as the pressure. But when no condensation of gas takes place, 
and the quantity is accurately as the pressure, to call this a case of 
affinity seems to me just as reasonable as to ascribe the air in a sand- 
hill to the chemical affinity of sand for air, and to argue that that 
affinity varies according to the state of the barometer. 
It may not be amiss to sum up these remarks under a few heads, 
exhibiting the leading principles of the theory of absorption which 
J adopt, in order that they may be more clearly understood, The 
gases are of course chiefly those of which water does not take more 
than its bulk. 
1, The quantity of any pure gas which water absorbs is in propor- 
tion to the pressure or density of the gas, 
