a Professors W. B. and R. E'. Rogers 
shaking for thirty minutes, this result is attained so perfectly, 
that no prolonged exposure afterwards indicates a continuance 0 
the absorption. The importance of attending to this point in 
constructing an apparatus for experiments in absorption, is evi- 
dent from the fact that while by our observation, which occupied 
generally less than thirty minutes, sulphuric acid of common 
density was found to absorb 98 per cent. of its volume of the gas; 
Saussure’s experiments, which continued for one or more days, 
make the absorption only 45 per cent. 
The difficulty and uncertainty of the method above mentioned, 
is moreover increased by the necessity of restoring the instrument 
to the standard temperature before measuring the absorption, and 
of taking account of the change of barometric pressure in the 
method is inadmissible where we are operating with liquids, 
which like nitric acid and many saline solutions react with 
ercury. 
Results as little satisfactory attended our trials with the other 
process of Saussure. In this mode of operating, which he adopted 
in cases whete the absorption was small, the liquid and gas are 
brought together in a well stopped bottle, and after continued 
agitation for some time, the absorption is measured by removing 
the stopper in an immersed position. But here, besides the diffi- 
eulty of making the absorption in a precise manner, we encounter 
a more serious objection in the fact, that the rarefaction of the 
remaining gas causes the absorption to cease before reaching the 
full amount proper to an undiminished pressure. This evil may, 
it is true, be rendered insignificant in cases where the absorption 
is slight, by using as Saussure did, a volume of gas many times 
greater than that of the liquid; but with carbonic acid, such a 
procedure would in most cases call for so large a volume of gas 
as greatly to increase the errors arising from a slight variation of 
temperature during the experiment, while it would augment the 
difficulty of securing the coincidence of temperature required. 
In the syphon formed apparatus used by Dr. Henry, the flexi- 
ble tube beneath, facilitates the experiment by enabling the ope- 
ator to apply agitation to the wider limb containing the gas 
liquid, but the results are exposed to error from the dilation of 
the flexible connection and from the effects of concussive com- 
pression caused by shaking a large mass of mereury with the gas 
and absorbent liquid. Of course, this method is inapplicable 
where the liquid reacts upon the mercury. 
From what has now been stated, it will we think be apparent 
that the modes of experimenting on this subject, used by the dis- 
