92 Proceedings of Royal Society of Edinburgh. [sess. 
At first sight these results appear very satisfactory, the nearly 
constant values obtained for any single solution indicating that the 
reaction was really monomolecular, while the different values for 
different solutions showed the effect of the various substances 
added. When the results are examined critically, however, especi- 
ally those from the two acid solutions Y. and VI., difficulties are 
encountered. In the two cases mentioned the end points are 
different from the remaining ones and from one another. The 
discrepancy is greater with nitric acid than with sulphuric acid, as 
would be expected from the greater ionisation of the former. 
Though the discrepancies are not very great, they indicate a con- 
siderable amount of action other than that resulting in the formation 
of nitric acid. Examination of the two equations 
(b) NH 4 * + 4S 2 0 8 " + 3H 2 0 = 10H' + 8S0 4 " + N0 8 ' 
(/) 4S 2 0 s " + 4H 2 0= 8H’ + 8S0 4 " + 20 2 
shows that the second action produces only one-fifth less acid 
than the first. Assuming that in solution I. the ultimate acidity 
(15 '34) was wholly produced by the first action, the acidity which 
would have been produced by the second action alone would 
have been 3 ‘07 less than this. In solution Y. therefore it may he 
assumed that one-fourth of the total persulphate had decomposed 
without producing nitric acid; in the case of the sulphuric acid 
solution VI., the proportion would he about one-sixth of the total. 
The higher rate of increase in the acidity in solutions Y. and YI. 
would therefore seem to be due, not to an acceleration of the action 
producing silver peroxide, but to the superposition of another 
action (apparently negligible in the other cases) similar to that 
which takes place in solutions of persulphate free from silver. It 
might have been expected that the acid gradually produced in, 
say, solution I. would result in bringing about the second of the 
above actions ; but, if the effect in that case had been appreciable, 
it is to be presumed that in solutions II. , III. and IV., to which 
neutral salts had been added (and in which, therefore, the 
concentration of the hydrogen ions would be diminished), the 
effect would have been less marked, with the result that the 
final acidities in these cases would have been higher ; but this is 
not the case. Even in solution I. the concentration of hydrogen 
