Hartitty—Wolecular Constitution of Supersaturated Solutions. 533 
Ewidence from Coloured Salts. 
In a Paper recently published by the Society,! evidence is 
adduced of the existence, in solution, of salts in a definite state of 
hydration, and of changes in the state of hydration, following 
upon rise of temperature. A second contribution is in course of 
publication, “On the Conditions of Equilibrium of Deliquescent 
and Hygroscopic Salts, with respect to Atmospheric Moisture.” 
In both these investigations the remarkable behaviour of cupric 
bromide is described. This salt crystallizes at temperatures below 
15°5° C. as golden green, and also as rich dark green prisms, when 
of larger size, with the composition CuBr,'5H,O; it forms also a 
dihydrate CuBr,-2H,0, which is dull black, like charcoal, and an 
anhydrous salt, the crystals of which are black, with brilliant 
steely lustre. On concentrating the solution at or above 15°C., 
only the anhydrous salt can be obtained, and this only after a very 
high degree of concentration. The solution is black in thick layers, 
or of an intensely dark brown in thin layers. A saturated solution 
of cupric bromide was cooled by immersing the vessel containing 
it in ice. Its temperature fell to 2° C. without any sign of crystal- 
lization or solidification, and there was no change of colour by 
cooling. This latter fact indicates that the liquid had not under- 
gone any change in its constitution. As but a little further 
concentration would cause the mass to ‘solidify in the anhydrous 
condition, it appears as if this is a supersaturated solution of 
CuBr,. Subsequently the temperature sank to 0°1°C., still without 
undergoing any change. On agitating the liquid by using the 
thermometer as a stirrer, it first deposited a few isolated golden 
green crystals of the salt Cubr."5H,O, and then solidified to a 
magma of crystals in the brown mother liquor when the tempera- 
was observed to rise to 38°C. These crystals could not be identified 
either with the pentahydrate or the anhydrous salt, and, as they 
were very perishable, they could not be submitted to any minute 
examination. Some of them were needle-shaped, and were probably 
small crystals of the pentahydrate; a larger proportion were 
rhombic plates, which is one of the forms of the anhydrous salt. 
1 Transactions, vol. vii., (Series II.) p. 253, 1900. 
