chemical change by measurement of the gases evolved. 585 
This experiment therefore enables to find the volume of oxygen 
liberated from the solution, or the amount of decomposition, at 
any definite time after mixing. 
Experiment II. This was performed in the same vessel, but 
without stirring, the quantities of the two solutions and the tem- 
perature remaining the same as before. After definite intervals 
of time 10 c.c. of the solution were withdrawn and titrated, and 
from these titrations the amounts of hydrogen peroxide decomposed 
were calculated. 
In the following table is given the results of these experiments. 
Time elapsed 
since mixing, 
minutes 
Available Oxygen 
left in solution, 
calculated from 
titration, .c.c. 
Experiment II. 
Volume of gas 
evolved, 
calculated from 
titration, c.c. 
Experiment II. 
Volume of gas 
evolved during 
experiment, c.c. 
Experiment I. 
0 
66 9 
0-0 
0-0 
3 
51-3 
15-6 
15-6 
6 
40-5 
26-4 
25-9 
11 
29-8 
37-1 
37-5 
21 
16 6 
50-3 
50-9 
33 
9-3 
58-6 
58-6 
The agreement of the last two columns, which represent the 
result of investigation of the reaction by titration and by deter- 
mination of the rate of evolution of gas from the agitated solution, 
is very close and furnishes a conclusive proof of the reliability of 
the latter method. 
It should here be mentioned that at the time these experiments 
were being performed Prof. Bredig of Heidelberg was working at 
the same subject ( Zeits.fur Electrochemie, II. 525). He proved 
that, when means are adopted to keep the solution in agitation, 
the rate of evolution of oxygen from a solution of hydrogen per- 
oxide with colloidal platinum is a true measure of the rate of 
decomposition of the hydrogen peroxide. Such agitation was 
produced by oscillating the reaction vessel which contained rods 
of glass. This method was found to answer well in this case, but 
I can scarcely think that it would be satisfactory in the case of 
more soluble gases such as carbon dioxide, or in the case of the 
evolution of carbon monoxide from sulphuric acid solution. In 
these cases my experiments have shown that very vigorous stirring 
is necessary to expel the whole of the supersaturated gas. 
