798 
MR. BRODIE ON THE CONDITION OF CERTAIN ELEMENTS 
I have now brought this investigation to that point at which for the present I shall 
leave it. I would willingly have attempted to render these tables of experiments 
more complete, had it not appeared to me that there were certain defects in the me- 
thod of experimenting which rendered this course unadvisable. One most important 
question is, whether the series of ratios by which I have expressed the relative loss of 
oxygen from the two substances is truly an intermittent or a continuous series, that 
is to say, whether there are or are not certain points where this ratio is constant 
although the proportions of the masses are varied. That there is with each chemical 
substance at least one such point, namely, a certain limit of reduction beyond which 
a great increase of the mass of the substance to be reduced does not alter the action, 
may, I think, be asserted with confidence, and without in any way implying that 
all the ratios which these experiments have brought to light are of this nature; yet it 
is difficult to account for the great coincidence of experiments made with very different 
proportions of the substances, without admitting a tendency of the action to fall into 
certain ratios rather than into others. Indeed the experiments appear to me to indi- 
cate both that for certain intervals the loss of oxygen truly does vary directly with the 
mass of the substance reduced, and that in certain other points the mass may be varied 
and the loss yet be constant. In these experiments, however, I could never secure 
that perfect agreement between two experiments made under exactly similar circum- 
stances, by which alone I could hope to answer a question demanding such exactness. 
One principal reason of the anomalies which the experiments occasionally exhibit is 
doubtless, that by simply mixing the substances, even where the same quantities are 
taken in two experiments, the same conditions of mass are yet not realized: I therefore 
turned my attention to other methods of experimenting, by which it is my hope to 
answer this question in a more exact and satisfactory manner. My experiments are 
not yet complete, but I may mention, that by operating with solutions, I have 
obviated this difficulty. Lastly, let me thus sum up the general results of these ex- 
periments. First, the amount of oxygen lost by the substance reduced is, under cir- 
cumstances otherwise similar, in a definite and constant ratio to the quantity of the 
peroxide of barium employed. Secondly, this loss is greater as the mass of the sub- 
stance reduced is increased, and diminishes as the temperature at which the reduc- 
tion takes place is raised. It varies also with the preparation of the peroxide. Thirdly, 
in each series of experiments there is a certain definite limit of reduction beyond which 
at any rate a very great increase of the mass of the substance reduced causes no in- 
crease of the loss of oxygen*. Lastly, in reference to that chemical question from 
which this inquiry proceeded, namely, how much oxygen is lost by the substance re- 
duced in proportion to the loss of oxygen from the peroxide of barium, it is to be ob- 
served, that however much the circumstances are varied, there are yet two limiting 
* It appears from other experiments which I have made, that with each chemical substance there is a spe- 
cific limit of reduction of this kind; thus, for example, in the experiment with chromic acid (p. 779), the only 
reason of the constant reaction there obtained, is that by taking a very great excess of the bichromate of potash. 
