Hartiey—WVolecular Constitution of Supersaturated Solutions. 585 
the temperature rose about 3° C. owing to the heat evolved in the 
act of combination, a proportion of the salt redissolved and 
remained in solution as CuBr. 
Attempts were then made to obtain a supersaturated solution 
of cobalt chloride which would crystallize suddenly. Several 
erystalline masses of the solid CoCl,-6H,O were placed in a tube 
and moistened with about 5c.c. of water; then boiled, and the tube 
plugged with cotton wool as soon as steam escaped freely from the 
mouth of the tube. The solution was then quite blue, and it was 
allowed to cool. The uppermost layer of the liquid touching the 
glass appeared purple, the bubbles upon it were crimson, but the 
liquid below, when shaken up, was indigo-blue in colour and very 
dark. After two trials, another solution was made which remained 
for about four hours in a test-tube cooling, but it did not acquire 
the colour of the cold solution obtained by saturating cold water 
at 15°C. It was purple like a solution when heated to 53°C. 
This solution had a boiling point of 115° C. It was evident that the 
cobalt chloride in the liquid had not resumed the condition of a 
salt with the composition of CoCl,"6H,O ; otherwise it would have 
resumed its colour. Some crystals had separated and adhered to 
the glass, though the tube was plugged with cotton wool and had 
not been opened. It appears, therefore, that no supersaturated 
solution of the original salt could be preserved for any length of 
time. The crystals which separated were red and quite unlike 
the solution, though their colour was precisely the same as that of 
the solid hexahydrated salt, which they proved to be. After 
leaving the purple solution which had been poured off from the 
crystals for twenty-one hours the colour became deep crimson, 
darker than the crystals which had been deposited within it, 
and also darker than the saturated solution of cobalt chloride, 
CoCl,'6HO, which had been kept for some days at temperatures 
varying between 15° and 20°C. It appears, therefore, that the 
water dissociated by rise of temperature had not all recombined 
with the salt to form the original hydrate, but that some compound 
intermediate between this and the anhydrous salt was the 
substance which remained in solution. From the colour of 
the solution the state of hydration of the dissolved salt was 
CoCl,4H,0. 
The theory which I had formed of the constitution of 
SCIENT. PROC. R.D.S,, VOL. 1X., PARTIV. 28 
