AT THE MOMENT OF CHEMICAL CHANGE. 
783 
serve the effect of varying the mass, at a constant temperature, and with the same 
preparation of the peroxide. 
The great accuracy of the silver determination and the comparative facility of de- 
termining by it the loss of oxygen from the compounds of this metal, caused me to 
confine to them my attention. Indeed it was plain from experiments I had made 
with the oxide of mercury, as well as with peroxide of lead, that the general nature of 
the changes in question was, with any one of these substances, the same. 
The following experiments were made with the chloride and the oxide of silver at 
100°, and at the temperature of the air : I had already found how very greatly at the 
lower temperature this circumstance might be varied without alteration of the action ; 
and in this case the experiments are arranged without any special reference to the slight 
variations of the temperature of the air. The peroxide taken is the same for each 
series ; the general form of the experiments was precisely as already described. 
Oxygen determinations. 
The determinations of the oxygen in the different preparations of the peroxide of 
barium employed, gave the following results : — 
I. Peroxide P. 
I. — (1.) 2'8970grms. of a peroxide (P) gave with hydrochloric acid and bichromate 
of potash, a total loss of 0'425 grm. of oxygen, corresponding to a loss of 14-67 per 
cent, on the peroxide. 
(2.) 2-9215 grms. of the same substance gave, in a similar experiment, a total loss 
of 0-427 grm. of oxygen, corresponding to a loss of 14-61 per cent. 
The oxygen in 100 parts of the peroxide, calculated from the above experiments, is, — 
I. 11. 
8-38 8-36. 
(3.) 2-823 grms. of the same peroxide in an experiment with platinum and acetic 
acid, gave a loss of 0*235 grm., corresponding to a loss of 8-32 per cent, oxygen. 
The mean of these three experiments gives 8-35 as the per-centage of oxygen in the 
substance. 
II. Peroxide Q. 
II. -(1.) 2-9565 grms. of a peroxide (Q) gave with hydrochloric acid and bichro- 
mate of potash, a total loss of 0-457 grm. of oxygen, corresponding to a loss of 15-45 
per cent. 
(2.) 2-9555 grms. of the same gave in a similar experiment, a total loss of 0-450 
grm. of oxygen, corresponding to a loss of 15-22 per cent. 
(3.) 2-955 grms. of the same gave with nitric acid and bichromate of potash, a total 
loss of 0-453 grm. of oxygen, corresponding to a loss of 15-32 per cent. 
The oxygen in 100 parts of the peroxide, calculated from the above experiments, is, — 
I. II. III. Mean. 
8-82 8-69 8-75 8-75 
