CHAP. X.] CONTINUITY OF THE CHALK. 521 
circumstances more favourable to the formation of this body than 
those which exist at the bottom of the ocean. The temperature 
is generally little over that of melting ice ; the pressure often 
exceeds several hundred atmospheres; whilst the carbonic acid, 
being produced gradually, and coming in statu nascendis in con- 
tact with the saline solution, is in the condition most favourable 
for easily entering into chemical combination. 
The amount of this salt formed depending on the pressure, it 
is evident that, on bringing up a sample of water from a great 
depth, a part of the carbonic acid, which was bound before, will 
become free under the atmospheric pressure ; and, moreover, as 
the amount decomposed varies with the time, it is evident that 
the amount of free carbonic acid, obtained by boiling in vacuo, 
will vary with the depths from which the sample was obtained, 
with the time it stands before boiling, with the temperature to 
which it is exposed during boiling, and with the duration of that 
operation. Hence it is easy to see how, assuming the body 
above mentioned to have been formed, Dr. Jacobsen found that 
the quantity of carbonic acid obtained by boiling in vacuo was 
no measure of the amount actually present, and that even 
portions of the same sample gave discordant results. 
It will be seen from the above remarks that solutions of car- 
bonic acid in sea-water and in blood resemble each other in 
almost every particular; only in the latter the retaining body is 
phosphate of soda, whilst in the former it is sulphate of mag- 
nesia, both of which contain constitutional water. The physical 
conditions, under which carbonic acid is eliminated from the 
blood and from sea-water, are also very similar. 
In the investigation of the behaviour of carbonic acid and 
of other gases to saline solutions, there is a practically unlimited 
field for useful research. The determination of the absorption 
coefficients of sulphate of magnesia solution for carbonic acid 
alone, under varying conditions of temperature, pressure, con- 
centration, and duration of action, would afford interesting and 
profitable occupation for more than one chemist. 
