1901 - 2 .] Action of Silver Salts on Ammonium Persulphate. 89 
concentration of persulphate ; for the silver will then be divided 
in a practically constant ratio between the two phases Ag’ and 
Ag 2 0 2 . Making this assumption, equation (c) becomes in effect 
monomolecular, for, if the reaction is irreversible, it is necessary 
to consider only the members on the left of the equation. The 
case is quite different with equation ( d ), for the concentrations both 
of H’ and of NH 4 * vary, that of the former starting from zero and 
increasing rapidly, while that of the latter diminishes. 
Preliminary experiments showed that, as was to be expected, 
change of temperature has a very marked effect on the rate of 
change ; at 50° the velocity is about eight times greater than it is 
at 25°. Also, the rate increases nearly, but not quite, proportion- 
ally, with increase of concentration of silver. As a result of the 
preliminary experiments, it was found most convenient to study 
the reaction in solutions which were 0*5 normal as regards 
ammonium persulphate and 0’0005 normal as regards silver; the 
solutions were kept in closed flasks placed in a thermostat at 25°. 
The choice of salts whose influence on the action could he studied 
is rather a limited one, halides being, of course, entirely excluded 
on account of the precipitation of insoluble silver salts. 
Six solutions were prepared as indicated in the following table, 
the quantities stated being dissolved, in each case, in one litre of 
solution. 
I. J(NH 4 ) 2 S 2 0 8 + ^oAgNO s 
II. J(NH 4 ) 2 S 2 O s + -joVoAgNOg + JNaNO, 
III. J(NH 4 ) 2 S 2 0 8 + W V» AgN0 3 + |(NH 4 ) 2 S0 4 
IY. !(NH 4 ) 2 S 2 O s + T J*o AgN0 3 + piI 2 XOg 
V. i(NH 4 ) 2 S 2 0 8 + W^AgY 0 3 + |HN 0 3 
YI. J(NH 4 ) 2 S 2 0 8 + ^AgN0g + iH 2 S0 4 
The course of the reaction was followed by removing, at 
intervals of twenty-four hours, 5 c.c. of each solution and titrating 
with jST / 5 alkali, using methyl orange as indicator. In presence of 
silver the indicator is rapidly bleached by the residual persulphate, 
but the difficulty was overcome by the addition of a drop of sodium 
chloride solution, which precipitated the silver. In the case of 
solutions Y. and YI. the initial acid concentration was determined 
