by Displacement in their own Mother-liguor. 39 



If we compare these two tables, we find the remarkable 

 result that while in the case of the potassium and the rubi- 

 dium salts the figures for the displacement in crystal are greater 

 than those for the displacement in mother-liquor, in the case 

 of the caesium salts the reverse is the case. 



Table VI. 



The Salt in Crystal and in Mother-liquor. 



K Eb Cs 



^ MR v 



(a) Values of -— — . 



D m 



7-010 6-641 — 6*711 CI 



5-422 7-422 — 0-317 Br 



5-074 3-411 —10-237 I 



(&) Values of -=— . — . 



D 17 



1-225 1-175 0-863 CI 



1-139 1-168 0-993 Br 



1-103 1-059 0-849 I 



MR v \ 



In Table YI (a) we have the difference — \ of the 



J D m) 



molecular displacement of the salt in crystal from its mean 



molecular displacement in mother-liquor. In compartment (h) 



, . /MR m\ . . 



we have the ratio ( ^=— . — ) of these quantities. 



Taking the figures in compartment (a) we see that in the 

 case of the salts of potassium and rubidium crystallization is 

 accompanied by considerable expansion, and this is what is 

 usually met with. In the case of the caesium salts the reverse 

 is the case, and very decidedly so in the case of the chloride 

 and of the iodide, much less so in the case of the bromide, 

 which, in this, as in other particulars, maintains its singular 

 position. 



In this connection it should be noted that among the ratios 



/MR m\ . ,,n i , -N 



( -yr- . —I given in compartment (o), the two which are near- 

 est to unity are those for Rbl (1-059) and for CsBr (0'993) 

 respectively; and their molcular weights are almost identical. 

 Further the salts situated co-diagonally to them, namely RbBr 

 and Csl, have ratios whose difference from unity are almost 

 equal, namely +0*168 for RbBr and —0-151 for Csl. 



Taking a general view of the figures in (h) which give the 

 ratios of displacement in crystal and in mother-liquor, we see 

 great differences. The most striking examples are, as in the 

 case of solubility, the extreme members of the ennead IvCl 



