1899-1900.] Dr Marshall on the Action of Silver Salts. 
163 
The Action of Silver Salts on Solution of Ammonium 
Persulphate. By Hugh Marshall, D.Sc. (With a Plate.) 
(Read February 5, 1900.) 
Although the action of potassium persulphate on silver nitrate 
solution was one of the first persulphate reactions observed, (vol. 
xviii. p. 64), I had not until lately paid any special attention to the 
behaviour of the ammonium salt in this respect. It appears, how- 
ever, that in the latter case there are additional actions of great 
interest, not possible with the potassium salt. A general description 
of these will be given now, but there are still some points deserving 
of further investigation. 
When solutions of potassium persulphate and silver nitrate are 
mixed, a black precipitate slowly forms, and this precipitate exhibits 
all the characteristics of silver peroxide. Apparently silver per- 
sulphate (which we may assume to he formed, to a certain extent, 
by double decomposition) is decomposed by water, like so many 
other silver salts of sulphur acids, by abstraction of S0 3 to form 
sulphuric acid. 
Ag 2 S 2 0 8 + 2H 2 0 = 2H 2 S0 4 + Ag 2 0 2 . 
In course of time the precipitate decomposes and dissolves with 
evolution of oxygen. 
When ammonium persulphate solution is mixed with silver 
nitrate solution a similar result is seen, hut only to a slight extent. 
Although there is very little deposition of peroxide, there is, how- 
ever, a considerable amount of decomposition, as shown by the 
formation of sulphate and free acid in the liquid. If ammonia is 
added to the mixed salt solutions there is no separation of peroxide, 
hut there is a much more rapid formation of sulphate accompanied 
with brisk effervescence. These reactions can he easily followed 
by starting with a pure persulphate solution and adding barium 
nitrate along with the other reagents. 
As it is known that silver peroxide oxidises ammonia to nitrogen, 
