846 
PEOFESSOE B. C. BEODIB ON THE OXIDATION AND 
Having ascertained, by preliminary experirhents which it is unnecessary to detail, that 
the quantity of peroxide of hydrogen decomposed by the same quantity of chromic acid 
was variable in amount, and depended upon the proportion in which the two substances 
were present, I instituted a series of experiments with the view of determining the 
law of this action. 
The absolute amount of the solution of peroxide of hydrogen employed in each experi- 
ment was the same, namely 20 P., or very nearly 100 cub. centims. This solution was made 
up of three parts ; of a standard solution of peroxide of hydrogen, of dilute hydrochloric 
acid, and of water. It is readily seen how, by means of the system of calibrated pipettes 
before mentioned, the bulk of this solution could be kept constant, while the amount of 
peroxide of hydrogen contained in it could be caused to vary. The hydrochloric acid 
employed was excessively dilute, and the same quantity of acid was used in each experi- 
ment. I ascertained, however, that the absolute amount of hydrochloric acid used had, 
within considerable limits, no appreciable influence on the reaction. Into this solution, 
which was contained in a small flask and kept in a state of rapid agitation dming the 
experiment, the solution of chromic acid was allowed to run freely from the pipette in 
which it was measured. After the first rapid evolution of oxygen had ceased, and the 
blue colour had disappeared, the solution was allowed to remain for 16 or 1 8 hours, and 
the excess of peroxide of hydrogen was then determined in the manner to be described. 
In dilute solutions a very considerable time is required for the completion of the reaction. 
When the chromic acid was in excess, the experiment was conducted in a precisely 
similar way, the solution of chromic acid being brought to the standard bulk of 20 P, 
The result was absolutely the same, whether the peroxide of hydrogen was gradually 
dropped into the chromic acid, or allowed to run freely from the pipette. On the effects 
of dilution and temperature I am not yet able to speak with precision ; but the solution 
may at any rate be considerably diluted (for example, mixed with an equal bulk of water) 
with no appreciable variation in the results. 
The value of the solutions of peroxide of hydrogen and of chromic acid employed, 
was determined by means of the same standard iodine solution and the excess present ; 
after the decomposition, of the peroxide of hydrogen or of chromic acid*, was also 
estimated in the same manner. 
Now, putting 
s=the parts of the iodine solution equivalent to 1 part of the solution of peroxide of 
hydrogen employed ; 
Sj = the parts of the same solution equivalent to I part of the solution of chromic acid 
employed ; 
* Chromic acid cannot he accurately estimated by this method if the solution be very dilute. In strong 
solutions the error is inappreciable, as I have ascertained by direct experiment. Similar difficulties occur 
if it be attempted to estimate directly a solution of peroxide of hydrogen by a standard solution ol 
sulphurous acid. To ensure an accurate result, the peroxide of hydrogen must be first decomposed by 
hydriodic acid, and the iodine formed estimated by sulphurous acid. 
