OXALATES, NITRATES* PHOSPHATES, SULPHATES, AND CHLORIDES. 
71 
which is not easily obtained in a crystallized state. This salt, however, is described 
as containing eighteen atoms of water, while the alums have twenty-four. At present 
I would merely throw out the conjecture, that in the alums we may have simply an 
alkaline sulphate with the sulphate of alumina attached, that salt carrying along with 
it its whole water of crystallization, and acquiring six atoms more. The quantity of 
water in potash alum may be reduced by efflorescence to six atoms in a stove of the 
temperature of 1 50° Fahr. Hence potash alum may perhaps be represented as follows : 
K S + (A1A1 S 3 ’ + 6 H + 18 II). 
I have shown by an analysis conducted in very favourable circumstances, that soda- 
alum contains, like potash-alum, twenty-four, and not twenty-six atoms of water. 
V. Of Chlorides. 
The affinity which the hydracids exhibit for water is weak. Of the lower hydrates 
of muriatic acid we know nothing, the volatility of the acid putting it out of em- 
power to form and examine such hydrates ; but it is likely that they will correspond 
with the hydrates of the chloride of magnesium, &c., which can be examined. 
The law in the case of the chlorides of the magnesian class of metals appears to 
be, that they have two atoms of water pretty strongly attached to them, and whicii 
we may consider as constitutional. Thus chloride of copper crystallizes with two atoms 
of water, and with no lower proportion ; but several chlorides of this class have two 
or four atoms more, the proportion of water advancing by a multiple of two atoms. 
1. Chloride of Copper. 
CuCl H2. 
The blue prismatic crystals of chloride of copper become brown and lose the 
greater proportion of their water at a temperature not exceeding the boiling point of 
water. Fifteen grains of the crystals, exposed to a much higher temperature, lost 
3*23 grains of water, leaving 11*77 grains of chloride of copper; and when this quan- 
tity of chloride of copper was exposed to the atmosphere, it quickly recovered 3*16 
grains of water, and resumed the blue colour of the crystallized salt. I believe this 
method of reabsorption, in the case of constitutional water, often to give hydrates of 
which the composition is even more exact than if they had been obtained from solu- 
tion, owing to the absence of that water, which is often mechanically interposed be- 
tween the plates of crystals. The hydrated chloride of copper obtained in this way 
consisted of 
Theory of CuCIH 2 . 
Chloride of copper . . . 11*77 100. 100. 
Water 3*16 26*85 26*84 
14*93 
126*85 
126*84. 
