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. 



