‘ a2 
On a New Method for the Determination of Atmospheric Carbon — 
Dioxide, based on the Rate of its Absorption by a Free Surface 
of a Solution of Caustic Alkah. 
By Horace T. Brown, F.R.S., and F. Escomse. 
(Received January 9,—Read March 23, 1905.) 
In an appendix to a paper on the static diffusion of gases, communicated 
to the Society in 1900,* it was shown that when a current of air containing a 
constant proportion of carbon dioxide is caused to move in a turbulent stream 
over the free surface of a solution of caustic alkali, the rate of absorption of that 
gas increases with the velocity of the air-current up to a certain optimal speed, 
beyond which no further increase in the speed of the current influences the 
rate of absorption. It was further shown that when the optimal velocity of 
the air-current has been reached, and the temperature is maintained practi- 
cally constant, the rate of absorption then varies directly as the partial 
pressure of the carbon dioxide in the air. In other words, if under the above 
conditions the rate of absorption per unit of area of the liquid surface is a 
for a partial pressure of carbon dioxide represented by y, and is a’ for a 
partial pressure of p’, then at similar temperatures, a/p = a’ /p’. 
A suggestion was also made that this principle might be found applicable 
to a determination of the carbon dioxide in air, and that if the method were 
found to be a practical one it would have the manifest advantage of not 
requiring any measurement of the air from which the gas was absorbed. 
Since the first account of our experiments we have made a more complete 
investigation of the principles underlying the proposed method, and have 
succeeded in determining the coefficient of absorption of carbon dioxide under 
these conditions, and also the manner in which this coefficient is influenced 
by temperature. When certain precautions are taken, this simplified method 
of determining atmospheric carbon dioxide gives good results, which in point 
of accuracy approach those obtained by the more elaborate method with the 
Reiset’s apparatus as described in the preceding paper. 
The absorption-apparatus used in the experiments was a slightly modified 
form of one given at 0, fig. 8) of *‘ Phil. Trans.’ B, Vol. 193) po2ee 
which is here reproduced with its present modifications. 
It consists of a glass cylinder A, about 15°5 cm. long and 6°5 cm. 
wide, closed with an india-rubber plug with a central perforation, through 
*® See ‘ Phil. Trans.,’ B, vol. 193, p. 282. 
