
1905.| Determination of Atmospheric Carbon Dioxide. 115 

proposition that under the conditions postulated, the rate of surface- 
_ absorption of carbon dioxide is proportional to the partial pressure of that gas 
in the moving air-current. 
A preliminary series of experiments, which need not be quoted here, had 
already established the fact that with this special form of apparatus, and with 
“amounts of carbon dioxide not exceeding about 14 parts per 10,000 of air, a 
velocity of current of about 150 litres per hour was sufficient to ensure 
a maximum rate of absorption. With the funnel adjusted to a distance of 
1 em. from the surface of the liquid, this corresponds to an average 
forward movement in the turbulent air-stream of about 260 metres per 
hour. 
In those cases where it was required to employ air containing less than the 
normal amount of carbon dioxide, part of the air was previously passed 
through a tower containing soda-lime, the necessary admixture with ordinary 
air being made on emergence from the tower before it was divided between 
the two forms of apparatus. When, on the other hand, air richer in carbon 
dioxide than ordinary air was required, the air stream was passed through a 
tower containing fragments of marble, on which there dropped a graduated 
flow of one-tenth normal hydrochloric acid. 
In the last two columns of the above Table are given side by side the 
- ratios of the partial pressures of the carbon dioxide in the air employed, and 
the ratios of the rates of absorption by the surface of the alkaline solution. 
It will be seen that these series of values are practically identical, thus 
clearly showing the direct relation between the partial pressures and the rates 
of absorption. 
The values given in the seventh column were obtained by dividing the 
number of cubic centimetres of carbon dioxide (measured at N. T. P.) 
absorbed per square centimetre of liquid surface per hour by the number of 
volumes of carbon dioxide contained in 10,000 volumes of dry air. The 
results represent the coefficient of absorption of carbon dioxide, stated in 
the form of cubic centimetres per square centimetre per hour, corresponding 
to a uniform partial pressure of 1/10000 of an atmosphere. Had there been 
an exact correspondence between partial pressure and rate of absorption in 
all these experiments, this coefficient would have been a constant. The 
variations which occur are largely due to differences of temperature ranging 
from 11°-2 to 15°-3 C. 
In order to investigate the influence of temperature on the rate of surface- 
absorption of carbon dioxide by soda-solutions, a separate series of experi- 
ments was undertaken, in which the absorption cylinder was immersed in 
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