Displacement in their own Mother -liquor 207 



that it furnishes more than the mere determination of the 

 specific gravity of the salt. Thus, by ascertaining almost 

 simultaneously the specific gravity of the mother-liquor and 

 the displacement in it of the crystals, both being at the tem- 

 perature of equilibrium, data are obtained for the determination 

 of the relation between the displacement of the salt in crystal 

 and its apparent displacement in saturated solution at that 

 temperature. It has not hitherto been permissible to make 

 exact comparisons of this kind owing to the independence of 

 the observations on the salt and on the solution, which have 

 been available. 



In discussing the results of observation it is convenient to 

 arrange them in a more articulate form than that of Table II 

 so as to bring each feature forward prominently and by itself. 



The group of salts which forms the subject of these experi- 

 ments is one of the most remarkable in nature. The salts are 

 nine in number and include all the possible binary combinations 

 of the members of the electro-positive triad K, Rb, Cs with 

 those of the electro-negative triad Cl, Br, I. The two triads 

 of simple bodies make three triads, or one ennead 1 of binary 

 compounds. The relations of the different members of the 

 ennead are best shown in a table of the form of Table III. 

 In it the salts of the same metal, A/, are all in one column, and 

 those of the same metalloid, R, all in one line. The symbol 

 MR represents both the formula and the molecular weight of 

 the salt 



TABLE III. Values of MR. 



K Kb Cs 



(a) Formula 



K( 1 RbCl CsCl Cl 



RW Br 



KI Rbl Csl I 



(h) Molecular weight 



74-6 121-0 168-5 Cl 



165-5 2I 3' 3 f 



166-1 i .:-5 260-0 1 



Compartment (a) of Table III contains the formula and 

 compartment (/;) the molecular weight of each salt. 



1 From the Greek frrrat, which signifies a body of nine. 



