Chemical Constitution of Saline Solutions. 281 
Notes on the Salts examined. 
Chromium Chlorides.—Chromium forms at least three chlorides, the anhydrous, 
Cr,Cl,, a lilac-coloured compound, is insoluble in water, but it slowly undergoes 
hydration, and then forms a green solution similar to that obtained when chromium 
hydroxide is dissolved in hydrochloric acid. But there are at least two varieties 
of the green chromic chloride, one precipitable by ammonium oxalate, the other 
not. 
Chromium Sulphate.—The following experiment shows that the green compound 
is formed when the violet solution is heated, 0°5 grs. of violet chromic sulphate 
were dissolved in 4 ¢.c. of water. A like quantity of the salt was converted into 
the green compound Cr,(SO,);5H,O by heating it in a water bath. It was 
dissolved in water, and made up to the same volume as the first solution. The two 
solutions were then examined in test-tubes of the same diameter. 
Chromic Nitrate, Cr3(NO;)'9H,0.—Ordway prepared this salt,* but it was 
also prepared and examined by me independently. Blue chromium hydroxide 
precipitated from chrome alum by ammonia was dissolved in nitric acid as long as 
the liquid remained blue. If it was seen to change to green, a little more nitric 
acid was added. ‘he liquid was evaporated in an air-pump bell-jar, but it was 
difficult to obtain a crop of crystals. After remaining for some time in a desiccator, 
a number of octahedral crystals were deposited. A second and larger quantity of 
liquid yielded only an ounce weight of crystals in the course of two years. The 
mother liquor frequently becomes green and uncrystallizable after it has arrived at 
such astage of concentration. The salt itself is of a deep violet colour; it becomes 
green at 36°, as Ordway has stated. It loses water of crystallization in a dry 
atmosphere and also at a very gentle heat. 
The remarkable change in the spectrum on heating is shown in figs. 1 and 2, 
plate XX.s. The green rays alone were transmitted by the hot solution, but 
only a narrow and sharply selected band of these. 
After cooling and keeping for some days the liquid had resumed its first 
condition and gave the original speetrum. 
This substance is evidently unchanged by heating to 100°. 
Experiments were then made with equal weights of the violet chromic nitrate, 
one portion being dissolved in water at 16°, the other being heated to 100°, and 
then dissolved in cold water (¢ = 18°), the two solutions being made up to equal 
volumes. 
The spectrum is practically the same as that of the nitrate solution at 100°; hence, 
the violet salt 1s converted into the green modification by heating the solution 
to 100°. 
* Phil. Mag., vol. 36, p. 205. 
