778 
MR. BRODIE ON THE CONDITION OF CERTAIN ELEMENTS 
The experiment with the acid solution of chromic acid was made thus : — a weighed 
quantity of the peroxide was mixed with a very large excess of powdered bichromate 
of potash in a small flask, such as is often used for the determination of carbonic 
acid, provided, that is, with a drying tube (in this case filled with small pieces of 
caustic potash) and a small tube reaching to the bottom of the flask, through which 
a little air might be drawn after the conclusion of the experiment. Strong hydro- 
chloric acid was contained in the usual small tube, and the whole experiment, in short, 
conducted precisely as a carbonic acid determination. It is essential to the accuracy 
of the experiment that care should be taken to have present a great excess of bichro- 
mate (at least three or four times the weight of the peroxide taken), an excess of 
acid, and also to have fresh potash in the drying tube, as there is a considerable rush of 
gas, and a little carbonic acid or water might otherwise pass through the tube. The 
peroxide, however, in a good preparation contains a mere trace of carbonate ; and I 
have made the experiment of passing the gas from the potash tube through baryta 
water, and have found that no carbonic acid escaped the apparatus, with a far more 
violent evolution of gas than need take place in the experiment. 
I. 2T015 grms. of the preparation A. gave a loss of 0*243 grm., corresponding to a 
loss of 1T56 on 100 parts of the substance taken. 
II. 2*1265 grms. of the preparation A. gave a loss of 0*252 grm., corresponding to 
a loss of 11*85 on 100 parts of the substance. 
III. 2*2127 grms. of the preparation B. gave a loss of 0*268 grm. corresponding 
to a loss of 12*11 on 100 parts of the substance. 
IV. 2*0975 grms. of the preparation B. gave a loss of 0*259 grm., corresponding 
to a loss of 12*34 on 100 parts of the substance. 
V. 2*0395 grms. of the preparation B. gave a loss of 0*243 grm., corresponding to 
a loss of 11*91 on 100 parts of the substance. 
From these experiments it results that in this reaction the chromic acid loses three 
and the peroxide four equivalents of oxygen, that is, that the total loss is to the loss 
from the peroxide as 7 *• 4. For calculating on this hypothesis the amount of oxygen 
in the two preparations, we find for the preparation A. from experiments I. and II. 
respectively, 6*60 and 6*67 per cent, of oxygen, and for the preparation B. from ex- 
periments III., IV. and V., 6*91, 7'05 and 6*80 per cent, of oxygen, which are the 
numbers given in the other experiments. The reaction would therefore be repre- 
sented thus — 
2Cr 03-{-4Ba 02=01*2 03-l-Oy-{-4BaO. 
This method has the advantage of giving a considerable loss of oxygen with a small 
quantity only of the substance ; and the perfect agreement with one another of nume- 
rous experiments made in this way, led me to place in it the greatest confidence. 
Facts, however, afterwards came to my knowledge, which proved that this action was 
not so absolutely uniform as had at first appeared ; and although under the circum- 
stances, and with the precautions (especially as to the relative quantities of the sub- 
