164 Scientific Proceedings, Royal Dublin Society. 
is voleanic, and that the gas has not reached us from interplane- 
tary space at all, because in that case the moon would have an 
atmosphere. 
He seeks to account for the vast quantities of carbonic anhy- 
dride of volcanic origin by the action of water trickling through 
the earth’s crust on to materials in its interior, of the nature of 
east iron, thus giving hydrocarbons, which by their combustion 
produced the gas. 
Dittmar’ has made an important contribution to the subject of 
the carbonic anhydride of sea water. From his exceedingly 
careful researches on its amount he came to the following con- 
clusions :— 
(1.) That free carbonic anhydride in sea water is the exception. 
As a rule, it is less than the proportion corresponding to bicar- 
bonates. 
(2.) In surface waters the proportion of carbonic anhydride 
increases when the temperature falls, and vice versd. 
(3.) Within equal ranges of temperature it seems to be lower 
in the surface water of the Pacific than it is in the surface water 
of the Atlantic Ocean. 
He also made experiments to determine the dissociation pressure 
of the bicarbonates in sea water, but with an artificial sea water. 
He found the tension to be about 0:0005 atmospheres, at tem- 
peratures which from recollection he fixed at 18-21° C., and 
considered that at 0° C. it would be 0:0003, which would corre- 
spond with the pressure of the gas in the air. 
[We gather from the memoir that this was a preliminary 
experiment of an investigation he proposed to continue, but we 
have not been able to find any account of further work, which 
was probably cut short by his death a few years later. | 
““T think,” he says. “that he (Schlesing) is right, but if so 
then the proportion of carbonic anhydride in the atmosphere should 
be more in the tropics than in the temperate zones and polar 
regions.” 
1 Dittmar, Challenger Reports, vol. i., Physics and Chemistry. See summary, 
p. 209. 
