1912-13.] The Absorption of Light by Inorganic Salts, No. IX. 139 
It had been intended originally to study the absorption spectra in 
alcohol and in acetone of the sulphates, nitrates, chlorides, and bromides 
of copper, nickel, and cobalt. The three sulphates when reduced to 
the anhydrous state were found insoluble. The nitrates, which were in 
the form of deliquescent crystals having the respective compositions 
Cu(N0 3 ) 2 • 3H 2 0, Ni(N0 3 ) 2 ■ 6H 2 0, and Co(N0 3 ) 2 * 6H 2 0, could not be obtained 
in the pure anhydrous state ; they fused readily on heating and decomposed 
before all the water of crystallisation could be driven off. The nickel 
chloride NiCl 2 6H 2 0 was, like the sulphates, found to be insoluble when 
dehydrated. The curves in the case of these four substances therefore give 
A for the salts in solution in a hydrated form ; but they were not dissolved 
in the form given above, the attempt being made to reduce them to lower 
states of hydration, and the values of A in these cases are put forward 
more from the qualitative than the quantitative point of view. In the 
case of these four substances the curves have much the same shape as 
for aqueous solutions, but the values of A are as a rule much higher. 
The other salts were dissolved in the anhydrous state, and the values 
of A are in this case more characteristic. The pale blue crystals of the 
dihydrate cupric chloride, CuC 1 2 2H 2 0, passed when heated through the 
green monohydrated phase to the rusty brown anhydrous salt, giving in 
alcohol an olive-green solution, and in acetone a yellowish-brown solution 
with a distinct new band in the violet. This solution, like most of those 
in acetone, did not keep well, turning rapidly to pale yellow and depositing 
a whitish crust. The cupric bromide, a black anhydrous powder, dissolved 
with great readiness in both solvents, producing in alcohol a black solution 
quite opaque except in very thin layers, when it appeared reddish brown. 
The acetone solution was lighter in colour and more transparent. 
The nickel bromide NiBr 2 • 3H 2 0 * was a light brown powder with traces 
of green. On heating, it darkened slightly and then turned yellowish, 
giving a turbid green solution in both solvents, with an insoluble yellowish 
residue. As with all the other alcoholic solutions of nickel, there was a 
rapid rise of absorption in the violet. 
The cobalt chloride consisted of hexahydrate crystals ; the anhydrous 
salt was a light blue powder giving in both solvents an intense blue 
solution. The bromide was in the form of dark crimson crystals of the 
hexahydrate, so deliquescent that they became liquid on exposure to the 
air. The anhydrous salt was bluish green, giving deep blue solutions, 
* We assumed this formula as it gave the percentage of water right. There is a 
trihydrate mentioned in Watt’s Dictionary of Chemistry. Hartley, however, describes only 
two hydrates, the dihydrate and the hexahydrate. 
