O34 Scientifie Proceedings, Royal Dublin Society. 
Two determinations of the water they contained yielded numbers 
from which 1:4 and 2°01 per cent. of water was calculated. This 
does not correspond to any molecular proportion; the salt was 
therefore a mixture of the anhydrous CuBr, with a crystalline 
hydrate. When the temperature had sunk again to 2°38° C., there 
was a larger proportion of mother liquor to crystals, as if a 
considerable proportion of the solid had re-entered into solu- 
tion. 
In order to render the condition of the solution such that the 
pentahydrate might crystallize out, there were added to the whole 
quantity of crystals and mother liquor together 10 c.c. of water. 
The black crystals dissolved, and the liquid became of a cold 
yellowish brown colour. Continued agitation of the liquid at a 
temperature of about 1° C. caused no indication of crystallization 
or change in colour. About 50 c.c. of the mother liquor, poured 
off the first batch of black crystals, were mixed with the above 
solution in order to concentrate it, and the mixture was cooled 
down to 0°5° C., with frequent vigorous stirring, but no crystalli- 
zation took place. The syrupy reddish brown solution drained 
from a mass of the black crystals, and which therefore was more 
concentrated than the yellowish-brown solution, did not show 
signs of crystallization after being kept for about two hours at a 
temperature of 0°5° C. with frequent stirring. 
It may be mentioned here that the thermometer, a very delicate 
one, each degree being divided into tenths, which was made by 
Casella many years ago, was tested after these experiments, and 
the zero was found to be only 0°2°C. too high. A second 
thermometer marking degrees only, made by Geissler, showed a 
similar error. 
The explanation of the phenomena, of which the foregoing is 
a detailed description, appears to me to be as follows. In the first 
instance, there was a completely saturated solution of the com- 
pound CuBr,. After cooling down below 15° C., the liquid wasa 
mixture of the dissolved anhydrous salt, with a small proportion 
of a solution of CuBr,5H,O0, which latter salt crystallized out. 
A portion of the water which held the salt CuBr, in solution 
having combined and formed the compound CuBr,-5H,O, the 
liquid then became a supersaturated solution of CuBr,, and the 
rhombic crystals of this compound were deposited. As, however, 
