XI. — On the Variation of Density with Concentration in 

 Weak Aqueous Solutions of Cobalt and Nickel 

 Sulphates. — By A. M. Morrison, B. A. 



(Beceivcd July 35th, 1S91.) 



In a paper which I had the honor of reading before the Insti- 

 tute last session * I g-ave tlie results of a short series of observa- 

 tions of the density of weak aqueous solutions of Cobalt Sulphate. 

 The solutions used were prepared Ijy mixing weighed quantities 

 of water and of crystals of the salt, which, on what seemed to be 

 satisfactory information, w^ere taken to be heptahydrated 

 crystals. The amounts of anhydrous salt present in the solu- 

 tions used were calculated on this assumption. 



On comparing the differences between the specific volumes of 

 these solutions and the volumes, in the free state, of their con- 

 stituent water, with similar differences in the case of solutions of 

 other sulphates, as determined by Prof. MacGregor,-|- it was evi- 

 dent that either the dilute solutions of this salt exhibited the 

 phenomenon of contraction in a very remarkable manner, or that 

 the information on which I relied as to the constitution of the 

 crystals used was incorrect. I therefore made several careful 

 chemical analyses of the crystals and found that they contained 

 not seven but six molecules of water. 



This beinp- so, the constitutions of the solutions whose densities 

 are given in the paper referred to, are consequently inaccurately 

 specified. I have therefore re-calculated them, and the results are 

 given in tlie first two columns of the following table : 



*Ti-ans. N. S. Inst. Nat. Sci., Vol. VH (1S90) p. 4S0. 

 [Trans. Roy. Soc. Can , Vol. VIU (1S90) Sec. iii, p. 19. 



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