306 Proceedings of Royal Society of Edinburgh. [sess. 
were obtained when common ammonium alum was employed in 
place of the chrome alum. 
These results seem to indicate conclusively that thallic sulphate 
does not form alums.* 
Thallic Sulphates. 
My experience in trying to prepare thallic sulphate from thallic 
hydroxide and sulphuric acid was very similar to that of Willm. f 
Well-formed crystals of a basic salt were easily obtained from the 
solution, but in none of the experiments was a normal salt obtained, 
no matter what acid concentration was employed. Willm gives 
the formula of the most hydrated salt obtained by him as 
T1 2 0(S0 4 ) 2 ,5H 2 0 . Several analyses made by me gave somewhat 
higher percentages of water than corresponds with this formula, 
and seemed rather to indicate a hexahydrate. As one molecule of 
water is retained above 100°, the salt is probably a hydroxy- 
sulphate, and, adopting Willm’s proportion of water, the formula 
might then be written T10HS0 4 ,2H 2 0 . 
As stated by Willm, the addition of concentrated sulphuric acid 
to a solution of this salt in dilute sulphuric acid produces a granular 
precipitate, still consisting of basic salt, but generally less hydrated 
than the above. Only on one occasion did I succeed in obtaining 
a different sulphate. This separated from a small quantity of 
solution in large clear crystals, very soft and entirely different 
from any others. The substance, after being powdered and placed 
in a stoppered tube, gradually deliquesced to an oily liquid. From 
determinations of T1 and S0 4 the composition of the salt corresponds 
to the formula HT1(S0 4 ) 2 ,4H 2 0 or 5H 2 0. The water was not 
determined directly. This acid salt may be looked upon as the 
acid from which are derived a series of well-defined double salts. 
An attempt was made to prepare thallic sulphate by electrolysis 
of an acid solution of thallous sulphate (kept saturated with the 
latter salt) in the manner employed by me for the preparation of 
oobaltic sulphate. £ A sparingly soluble thallous-thallic sulphate 
was obtained, which will be described later. 
* Statements to the contrary are occasionally met with in text-books. 
t Ann. Chim. Phys. [4], v. p. 28 (1865). 
X Chem. Soc. Trans., lix. p. 760 (1891). 
