On the Nature of Solution. 473 



r»B r*c r*A 

 arcs, which we shall denote by 1 ds, I ds, \ ds, we find for 



(2) Ja Jb Jc 



C^r°ds + r*ds 



Ja P Jb P Jc P 



But I — is the change of direction in the arc A B, and 

 Ja P 



similarly for the two others : hence the theorem. 



LVII. On the Nature of Solution. By J. Alfked Wanklyn, 

 W. Johnstone, and W. J. Cooper*. 



THE venerable Dalton made the great discovery, about the 

 year 1840, that contraction occurs when salts dissolve 

 in water. In some instances the contraction is so great that 

 the volume of the solution of the salt is not greater than that 

 of the water itself — the contraction being as large as the 

 volume of the anhydrous salt existing in the solution. Dalton 

 experimented upon the same salt in its hydrated and in its 

 anhydrous condition, and he also extended his investigation 

 to a great variety of salts, and his results he sums up as 

 follows! : — " I have tried the carbonates, the sulphates, the 

 nitrates, the muriates or chlorides, the phosphates, the arse- 

 niates, the oxalates, the citrates, the tartrates, the acetates, 

 &c, &c, and have been uniformly successful : only the water 

 adds to the bulk, and the solid matter adds to the weight." 



Such was the condition in which Dalton left this subject 

 about the year 1840. 



Taking up the investigation where Dalton left off, we find 

 that in the majority of cases there is indeed considerable con- 

 traction when salts dissolve in water, but that the degree of 

 contraction varies very widely with different salts. In some 

 instances in which mineral matter dissolves in water, the 

 contraction is so great that the volume of the solution is 

 actually less than the volume of the water which forms it. 

 This is strikingly exemplified by lime-water, which occupies 

 less space than the water which it contains. On the other 

 hand, there are cases where the volume of the solution of a 

 mineral salt is almost as great as the sum of the volume of the 

 salt plus the volume of the water in the solution. (The solu- 

 tion of nitrate of silver is a case in point.) There are even 

 instances where expansion takes place. This is exemplified 



* Communicated by the Authors. 



t Henry's 'Life of Dalton/- (Cavendish Society), p. .193.. . . 



