536 
Richards. — The Respiration of 
make quite sure of a pure sample of the gas in the receiver. 
The samples of gas for analysis were collected in little tubes 
over dry mercury. After each experiment the air was renewed, 
either by running a strong current of air through the receiver, or 
by removing the plants from the bottle and filling it with water. 
As a control for the method, experiments were made with 
samples of air containing a known quantity of C0 2 . This 
was analyzed at the beginning of the experiment, and again 
two days later, after the apparatus had been under water as 
described. As will be seen below in the three analyses given, 
the percentage of C0 2 does not vary appreciably between the 
beginning and end of the experiments : — 
No. of experiment . 
I. 
ll. 
III. 
% C 0 2 at beginning 
5 *94 
ii-35 
8^42 
% C0 2 48 hours afterwards . 
5'9 2 
n-37 
00 
Oj 
00 
The danger of leakage as 
a source of 
error 
having 
shown to play no part, the only other errors to be considered 
are those possibly arising from change of temperature during 
the course of the experiment, or from the danger of the air in 
the capillary delivery-tube vitiating the sample taken ; but 
these were guarded against in the manner described. While 
the plants under experiment were plentifully supplied with 
moisture, care was taken to allow no considerable amount of 
water to remain in the receiver, as a source of error due to the 
absorption of C0 2 thereby might arise. The agreement of 
the results among themselves speaks for the accuracy of the 
methods employed. 
For the analysis of the air one of the improved Bonnier 
and Magnin apparatuses was used, such as is described by 
Aubert 1 . By observing all the precautions against errors 
described by the above writers, it is possible to obtain results 
of more than sufficient accuracy for this work, and a similarity 
of manipulation tends to equalize any other remaining sources 
of error. Repeated analyses of the air in the laboratory 
showed that, as far as the purposes of this research are con- 
cerned, the amount of C0 2 contained in it need not be 
1 Rev. Gen. de Botanique, Vol. iii, p. 97, 1891. 
