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On the Variations in the Amount of Carbon Dioxide in the Air of 
Kew during the Years 1898-1901. 
By Horace T. Brown, F.R.S., and F. Escomse. 
Received January 9,—Read March 23,, 1905. 
As part of the routine work connected with our investigation of the 
processes of photosynthesis in plants, an account of which has been given in 
a previous series of papers, it became necessary from time to time to make 
a large number of determinations of the amount of carbon dioxide present in 
the air. 
Since these determinations were made by a method which admits of a high 
degree of accuracy, and also extend over a considerable period, we have 
considered it desirable to collect the results, which are valuable in showing 
he limits of variation in the amount of this constituent of the atmosphere, of 
which « somewhat fallacious idea has been frequently entertained. 
The method of experiment has already been described in a previous paper,” 
and it will, therefore, suffice to say that it consists in the absorption of the 
carbon dioxide from about 100 to 300 litres of air by means of a solution of 
sodium hydroxide contained ina Reiset’s absorption apparatus, the amount 
of absorbed gas being subsequently determined by a process of double 
titration. 
The experimental error incidental to the method falls well within + or 
—1 per cent. of the total amount of carbon dioxide estimated, so that the 
numbers representing the volumes of carbon dioxide per 10,000 volumes of 
air have certainly not a larger error than 0:03 parts per 10,000. 
The air was taken from outside the Jodrell Laboratory in Kew Gardens, 
at a height of 4 feet 6 inches from the ground, and without any previous 
filtration. 
The results, expressed in volumes of carbon dioxide per 10,000 volumes of 
dry air, have been thrown into a tabular form at the end of this paper, the 
date of each observation being given. (See Table II.) 
The average value for the 91 experiments recorded is 2°94 volumes of 
carbon dioxide per 10,000 of air. The lowest value obtained (August 9, 1898) 
was 2:43, and the highest (March 16, 1899) was 3°60 per 10,000. This latter 
result, obtained during a fog, was a very exceptional one, and out of the whole 
* © Roy. Soc. Proc.,’ this vol., p. 33. 
