1901 - 2 .] Dr Hugh Marshall on Thallic Sulphates. 
307 
Ammonium Thallic Sulphates. 
As the experiments with thallic sulphate alone were so far not 
very satisfactory it was decided to examine the double salts, in the 
hope that they would give information which might help to eluci- 
date the mystery concerning the formation of the normal salt. A 
number of double salts have been described by previous investiga- 
tors, but as the ammonium derivatives had apparently escaped 
attention a beginning was made with these. 
Solid ammonium sulphate was added to the mother liquors from 
a preparation of basic thallic sulphate, and the liquid was warmed. 
As the crystals dissolved,,., a firie granular precipitate began to form 
and increased to a considerable quantity, remaining even when 
the liquid was heated to boiling. The substance, drained and 
dried between filter paper, gave on analysis results showing it to 
be an anhydrous double sulphate, corresponding to the formula 
NH 4 T1(S0 4 ) 2 . 
Though sparingly soluble in the acid liquid containing a large 
excess of ammonium sulphate, this double salt is easily soluble in 
dilute sulphuric acid. (Like all the thallic salts it is hydrolysed by 
water.) When this solution is allowed to evaporate at the ordinary 
temperature it deposits fairly large colourless crystals of prismatic 
habit, apparently monoclinic ; their composition is represented by 
the formula NH 4 T1(S0 4 ) 2 ,4H 2 0 . The quantity of water found 
on analysis is rather less than this, but, as the crystals effloresce at 
the ordinary temperature, this is to be expected. 
When an acid solution of thallic sulphate, or of the above double 
sulphate, is saturated with ammonium sulphate at the ordinary tem- 
perature, crystals of a totally different appearance are gradually 
formed. They are translucent, soft, and rather indefinite as 
regards crystalline character, and resemble fine crystal aggregates 
rather than distinct crystals. Their composition corresponds to 
the formula (NH 4 ) 3 T1(S0 4 J 3 . When treated with dilute sulphuric 
acid they yield a solution which, on spontaneous evaporation 
at the ordinary temperature, yields the above-mentioned salt 
NH 4 T1(S0 4 ) 2 ,41I 2 0. 
