ART. XVI.—NOTE ON THE VARIATION OF DENSITY WITH CON- 
CENTRATION IN WEAK AQUEOUS SOLUTIONS OF 
CoBALT SULPHATE.—_-By A. M. Morrison, B. A. 
(Read 12th May, 1890.) 
In a paper by your President, read before the Royal Society 
of Canada in 1885, and in another by the same author, read 
before the same Society in 1889, it was pointed out that, in suffi- 
ciently weak aqueous solutions of certain salts, the excess of their 
density over that of water at the same temperature, is very 
nearly proportioned to the mass of salt they contain. Or, in 
symbols, D,=d,+k p, where D, represents the density of the 
solution, i. e., the mass in grammes of 1 cu. cm. of it, at the tem- 
perature 7°; d,, the density of water at ?¢°; p, the percentage of 
anhydrous salt in the solution, and k, a constant for any given 
substance and temperature. 
It was for the purpose of discovering to what extent this is 
true for Cobalt Sulphate, which was not mentioned in the papers 
cited above, that the following determinations were made. 
The solutions were formed by mixing weighed quantities of 
crystallised Cobalt Sulphate (Co SO,+7 H.O) with weighed 
quantities of water. The salt was purchased as pure from Queen 
& UCo., Philadelphia. It was found to be free from mechanical 
and was assumed to be free from chemical impurities. Only 
clear, well-formed crystals were used so as to make sure that 
each elementary crystal contained exactly seven molecules of 
water. 
A new solution with freshly-distilled water, boiled to drive out 
air, was made for every determination; for it was found that 
solutions left standing a day or so threw down sufficient precipi- 
tate to interfere seriously with the correct working. 
All weighings were made in stoppered bottles, by the method 
of “ double weighing,” and were, of course, reduced to “7m vacuo.” 
The relative errors of the standard weights employed were neg- 
lected. The balance was a delicate one by Collot, of Paris. In 
481 
