on the Nature of Solution. 475 



overflows will be : and the increment of weight in that 



case wonld be S P* S 1, 



i — L-. 



sp. gr. 

 Such a value we represent by ?\. 



1 



sp. gr. 



This is the case of sugar, and no doubt of many organic 

 substances which simply dissolve in water without chemical 

 action of any kind. 



(2) There may be contraction. This is exemplified by 

 common salt and water. When one gramme of common salt 

 is inserted into 100 cub. centim. of water, the displaced water 

 is partly condensed and retained in the 100 cub. centim. 



i — i x =. the condensate ; 



that is to say, the weight of the water which, instead of 

 overflowing, is retained in the vessel when one gramme of 

 .salt dissolves so as to give 100 cub. centim. of the solution. 



(3) There may be expansion. In such a case when one 

 gramme enters the 100 cub. centim. or the litre a larger 



quantity than will overflow and 



J sp. gr. 



i— i x becomes a, minus quantity. 



This is exemplified by chloride of ammonium, which under- 

 goes decomposition when it is dissolved in water, and the 

 volume of the solution of that salt actually exceeds the sum 

 of the volumes of the water and the salt in their separate 

 condition. 



In a series of papers which have recently appeared in the 

 • Chemical Xews,' we have treated solution from this point of 

 vie w } and shown that the condensate (i — ij, in the case of 

 very many salts, bears an atomic relation to the gramme of 

 salt which occasions it. 



Sugar and Water. 



The ordinary tables of the specific gravities of solutions of 

 different strengths are constructed so as to mask the regu- 

 larity of the relation between specific gravity and strength. 

 The common sugar table, for instance, gives the specific 

 gravities corresponding to the strength represented in per- 

 centage by weight. That mode of statement hides the regu- 

 larity ; but when the table is transformed so as to set out 



