1901-2.] Dr Hugh Marshall on Thallic Sulphates. 
309 
sulphate, the mother liquor from the granular precipitate, when 
allowed to stand at the ordinary temperature, deposits colourless 
prismatic crystals of the hydrated normal salt ; it is therefore 
probable that the normal salt could be obtained directly from a 
thallic sulphate solution by using potassium sulphate in small quan- 
tity only. 
A simple method of preparing the basic salt consists in heating 
together thallous sulphate, potassium persulphate, and potassium 
carbonate, with a sufficient quantity of water ; evaporating, and 
then digesting the residue with dilute sulphuric acid. After re- 
peatedly exhausting with dilute sulphuric acid to remove any 
excess of potassium sulphate, the granular precipitate is drained 
and dried. 
Rubidium Thallic Sulphates. 
By mixing rubidium sulphate and thallic sulphate solutions and 
allowing the mixture to crystallise, either a granular anhydrous 
double sulphate RbTl(S0 4 ) 2 , or the hydrated salt RbTl(S0 4 ) 2 , 4H 2 0 
may be obtained, depending on the temperature and the acid 
concentration employed. The hydrated salt crystallises in clear 
colourless prisms resembling those of the corresponding ammonium 
and potassium salts. 
Thallous Thallic Sulphates. 
When attempting to prepare thallic sulphate by electrolysis 
(y. supra) a large quantity of a light-yellow finely crystalline 
powder was obtained ; analysis showed this to be the anhydrous 
double sulphate Tl5Tl"'(S0 4 ) 4 . (The corresponding iodide T1 3 I 4 
or T1 5 T1 I s is known.) The same double salt was also obtained as a 
product of decomposition from thallic sulphate residues which had 
stood for a considerable time exposed to the air. The dry salt 
underwent a distinct change of colour when kept in a closed tube, 
becoming much paler ; this is possibly due to its undergoing a 
transition into a mixture of other salts. 
A quantity of this double salt was dissolved in warm dilute nitric 
acid and allowed to crystallise ; the first crops of crystals, in fern- 
like aggregates, were found to be pure thallous nitrate. Thereafter, 
