and Attached Water. 



215 



not too symphonous 



with 



" equivalents." 



Say, 



therefore, w i 



worths." 





Temperature of 

 solidification of 







Salt. 





cryohydrate. 





Water-worth. 



Nal . 



, 



. . -15 





5-8 



NH 4 I . 



. 



. -27 





6-4 



NaBr . 



. 



. . -24 





8-2 



KI . . 



. 



. -23 





8-5 



NaCl . 



. 



. -23 





10-5 



NH 4 Br 



, 



. -17 





11-1 



NH 4 C1 



• 



. . -16 





124 



KBr . 



. 



. -13 





140 



KC1 . 



, 



. -11-4 





16-5 



It appears that, for the same halogen, a sodium salt attaches 

 less water than an ammonium salt, and the ammonium salt less 

 than the potassium salt. Also, for the same metal, an iodine salt 

 attaches less water than the bromine salt, and the latter less 

 than the chlorine salt. 



Or if we denote by W XM the number of molecules of water 

 attached to one molecule of XM, then 



and 



lNa< M, XNH 4 < tt 'XK, 



"IM ^BrM < M 'C1M. 



This remarkable rule has no exception amongst the above nine 

 and the only exception to the general rule, that the lower 

 the solidifying-point the fewer the molecules of associated water, 

 is offered by the iodide of sodium. Concerning this see § 68. 



§ 67. It may be perhaps more than accidental that the num- 

 bers of molecular water- worths show a distinct tendency to be 

 multiples of 0*5. For my own part, recognizing the possible 

 range of analytical error, I for the present distinctly forbear 

 to express any opinion as to whether we are here dealing 

 with the same physical force which constitutes chemical attrac- 

 tion, and which regulates the integral ratios of molecular com- 

 bination as most chemists appear to understand the term — or 

 whether it is a distinct or distinctly conditioned force binding 

 the salt and water together in quite a new ratio, or a ratio which 

 can only be brought to the chemical one by multiplication by 

 constants, at present arbitrary. 



It is useful, however, to reflect that almost innumerable in- 

 stances are known in which the molecular ratio between a salt 

 and its ordinary water of crystallization is not a simple one. 

 On examining the published determinations of water of crystal- 

 lization effected by the chemists who are or have been both ac- 



