373 
Dioxide Absorption of Coco-nut Leaves . 
The apparatus was started at 5.30 a.m., and determinations of car- 
bon dioxide absorption were made at two-hour intervals until 5.30 p.m. 
and again at 6.30 p.m. The results of the titrations of the samples ob- 
tained during these tests are given in Table I. Columns 2 and 3 show the 
amounts of acid required to neutralize the samples of barium hydroxide 
from the Pettenkofer tubes. Columns 4 and 5 show similar data for the 
corresponding barium hydroxide wash bottles. Column 6 shows the con- 
centration of the hydrochloric acid used in titration, and column 7 gives 
observations and notes made during the tests. 
The above data prove, first, that the difference in carbon dioxide 
content of the air leaving the test and control apparatus was inappreciable, 
since the titrations of the wash bottle solutions from test and control gave 
identical values for each period. This same uniformity in results from the 
wash bottles was obtained in all subsequent tests. The difference in titra- 
tion values of solutions from the Pettenkofer tubes of test and control 
therefore indicates the difference in carbon dioxide content of the air passing 
through these, and thus serves as an index of the carbon dioxide absorbed 
by the leaf in the test apparatus. 
The carbon dioxide absorption in grammes during each period is given 
in Table II (column 4). These values are all computed from the data of 
Table I. 
To test whether the carbon dioxide of the air is completely extracted 
by the barium hydroxide in the Pettenkofer tubes, the difference in con- 
centration between the Pettenkofer tube and wash bottle of the control for 
each period is computed to show the number of grammes of carbon dioxide 
absorbed per hour per c.m. of air (assuming that exactly 38 litres of air 
pass through the apparatus each two hours) (Table II, col. 2). This 
weight of carbon dioxide is then converted into terms of the number of 
parts by volume in 10,000 parts of the air, assuming a constant air tempera- 
ture of 27° C., which is very nearly an average day temperature in this 
locality. These values are given in Table II, col. 3, and are sufficiently 
close to the assumed average carbon dioxide content of the air (3 parts in 
10,000) to indicate that the carbon dioxide of the air was completely 
extracted. The calculated carbon dioxide content of the air was not found 
to be constant, but varied from 3 to 4 parts in 10,000. This variation is 
not surprising in view of the findings of Brown and Escombe, which show 
that the carbon dioxide content of the air near the earth varies as much as 
this. A part of this apparent variation in carbon dioxide content of the air 
may also have been due to variations in the rate of flow of the air through 
the apparatus from one period to another. Column 4 shows the difference 
in titration values between the control and the test apparatus. Column 5 
shows the amount of carbon dioxide absorbed by the leaf per square 
metre. 
