chemical change by measurement of the gases evolved. 607 
Hydrogen Peroxide. 
A similar series of experiments were performed in the case of 
the decomposition of hydrogen peroxide in the presence of col- 
loidal platinum. No change was made in the apparatus except 
that the stirrer and the interior of the reaction vessel were coated 
with a thin layer of paraffin wax as in the case of the earlier 
experiments with hydrogen peroxide. It was found that owing 
to the greater solubility of oxygen there was a correspondingly 
greater difference between the rates of evolution of the gas from 
the still and the agitated solution due to a larger volume of the 
gas remaining supersaturated in the solvent. 
The observations taken during these experiments are repre- 
sented graphically in Fig. 12. As before, the rate of evolution of 
gas from the supersaturated solution may be calculated in terms 
of the amount of gas stored up in the solution. The results 
obtained are given in the following table : 
Rate of evolution 
of gas, 
c.c. per minute 
Volume of gas 
stored in solution, 
c.c. 
Rate of evolution 
of gas, 
c.c. per minute 
Volume of gas 
stored in solution, 
c.c. 
0-61 
8-5 
1-5 
20-1 
0-76 
11-2 
1-6 
21-4 
0-87 
12-6 
1-7 
21-8 
104 
14-5 
1-48 
19-8 
1-2 
16-3 
1-34 
17-4 
1-36 
18-3 
1-1 
13-7 
If we take the solubility of oxygen to be '03 at 20 4, then 
the greatest amount of gas supersaturated in the solution is 
36 times the normal saturation volume of gas dissolved by the 
same volume of solution. 
It will be noticed that for a degree of supersaturation of 
30 times the normal amount dissolved by 20 c.c. of solution, 
the rate of evolution of oxygen gas is about 1*33 c.c. per minute. 
The rate of evolution of nitrogen at 62° from 20 c.c. of a solution 
whose degree of supersaturation is also 30 may be calculated to 
be about ‘32 c.c. per min. from the experiment described above. 
To make this result comparable with the value for oxygen we 
must multiply by 5 — the ratio of the solubility of oxygen at 20° 
to the assumed value '006 for the solubility of nitrogen at 62° — 
so as to obtain the rate of evolution for the same degree of super- 
saturation and the same volume of gas supersaturated in the 
