536 Scientific Proceedings, Royal Dublin Society. 
supersaturated solutions has been recently confirmed by M. G. 
Wyrouboff in a memoir, “ Recherches sur les Solutions.’ 
He has worked on four salts which form hydrates with dif- 
ferent proportions of water, and has investigated the solubility 
of these hydrates at different temperatures. These are nickel sul- 
phate, cerium sulphate, thorium sulphate, and potassium-cadmium 
sulphate. 
There are no fewer than four different forms of nickel 
sulphate : — (1) NiSO,.,7H.O, orthorhombic, emeraid green ; 
(2) NiSo,6H,O, cubic, bluish green; (3) NiSO,6H,0, clino- 
rhombic, yellowish green; (4) NiSO,5H,0, crystalline system 
not described, a bluish salt which effloresces. 
The solubility of these salts increases from the first to the 
third, which crystallizes at 70°C. The fourth salt is even more 
soluble; it is formed by evaporation at 100°C., and precipitation 
from the concentrated solution by the addition of alcohol. It has 
been shown by Lecocq de Boisbaudran that, by the introduction of 
a fragment of a erystal of CoSO,6H,0, or FeSO,6H,0, into a 
supersaturated solution of nickel sulphate, the clinorhombic form 
of the salt NiSO,6H,O is separated. ‘The interpretation of this 
phenomenon is, that the salt in solution is NiSO,dH,0, but 
the salt which crystallizes out is the clinorhombic NiSO,6H,0, 
which is less soluble. 
In 1887, Dr. W. W. J. Nicol? brought forward the view 
formerly advanced by Leewel,® that solutions usually regarded 
as supersaturated are not really so, but owe their formation to the 
fact that the salt dissolved is not the same as that which crystallizes 
out. He further states that no well authenticated cases of super- 
saturation of a solution of a salt which crystallizes without water 
is known to him. 
As I have already pointed out, the supersaturation of solutions 
of anhydrous compounds, which do not form crystalline hydrates, 
is not so considerable as to be a well-marked phenomenon even 
when the salt is much more soluble in hot than in cold water; and 
such supersaturated solutions do not exhibit the marked pecu- 
liarities characteristic of solutions of hydrated compounds—as, for 
Q0 
1 Bulletin de la Société Chimique de Paris, 3° serie, t. xxv.—xxvi., p. 105, 1901. 
2 Chem. Soc. Trans., vol. 51, p. 389. 
2 Ann.’Chem. Phys. [8], 49-51, 
