40 J. Y. Buchanan — Specific Gravity of Soluble Salts. 



and Csl. The former expands by more than 25 per cent, and 

 the latter contracts by 15 per cent on crystallizing. 



These figures accentuate the peculiarity of the caesium 

 salts, that crystallization is accompanied by contraction. An 

 interesting conclusion can be drawn from the behavior of the 

 different salts in this respect, namely, that the crystalliza- 

 tion of the potassium and rubidium salts of the ennead must 

 be hindered by increased pressure, while that of the caesium 

 salts must be helped by the same agency. 



Conclusion. — The method of determining the specific grav- 

 ity of a soluble salt in its own mother-liquor, as described in 

 the first part of the paper, involves manipulations of too deli- 

 cate a character to permit it to pass into general practice in 

 competition with other methods for the same primary pur- 

 pose. When, however, the specific gravity of the salt has 

 been ascertained in this way, the relation between its apparent 

 displacement in the state of crystal and in that of saturated 

 solution have been ascertained at the same time. In the sec- 

 ond part of the paper the observations are discussed from 

 this point of view, but owing to exigencies of space the dis- 

 cussion has been limited to the accentuation of the salient 

 features. One of the most important of these is the connec- 

 tion which reveals itself between the molecular weight of the 

 salts and their specific gravity and displacement in crystal and 

 in saturated solution, in definite conditions. The authority of 

 the periodic law makes itself as clearly felt in the limited area 

 of the ennead as it does in the realm of the elements. It is 

 true that the caesium salts introduce some irregularity into the 

 periodicity, but this is not to be looked on as an exception, but 

 as an interference, the nature of which it will be interesting 

 to trace. 



