390 Messrs. Wright and Thompson on the Determination of 





Zinc 



Copper 



Cadmium 





sulphate. 



sulphate. 



sulphate. 



n= -25 















•5 



1-8 



1-85 



1-75 



10 



4-25 



4-5 



4-0 



1-5 



6-35 



6-4 



5-95 



20 



8-0 



7-95 



74 



2-25 



8-65 



8-55 



7'95 



30 



108 





995 



40 



1295 





11-95 



50 



1505 





13-75 



55 



160 





14-5 



The curves marked respectively 1, 2, and 3 (fig. 7) represent 

 these values. It is evident that the contraction with cadmium 

 solutions is always less than that with zinc- or copper-sulphate 

 solutions, instead of greater, as might have been a priori anti- 

 cipated from the greater heat of dilution. The difference, how- 

 ever, is in no case very great ; whilst with zinc and copper 

 solutions the curves almost coincide. 



163. From these values the amounts of contraction on in- 

 termixture of gramme-molecules of two solutions of any one 

 of the three salts differing in strength are readily calculable 

 by the formula 



C — Ci + c 2 — 2c 3 , 



parallel with the analogous equation for heats of intermixture 

 (§ 160); where C is the contraction on intermixture, and c 1? 

 c 2 , and c 3 respectively the contractions on dilution to the same 

 ultimate limit of the solutions MSG 4 2aH 2 0, MS0 4 26H 2 0, 

 and MS0 4 (a-f&)H 2 ; and more generally still the contrac- 

 tions are calculable that ensue when any two solutions of 

 any pair of the three salts are intermixed. Thus, when A 

 gramme-molecules of MS0 4 ???H 2 and B gramme-molecules 

 of M/S0 4 nH 2 are intermixed, the resulting mixture is 



r - M -ls0 4 ^i±^H 2 0. 



wj 



A + B 



If, then, a be contraction per gramme-molecule on diluting 

 the first solution to the strength of the mixture, and b be the 

 (negative) contraction ensuing on (negatively) diluting the 

 second solution to the same strength, the total contraction on 

 intermixture is Aa+Bfi, and the contraction per gramme- 

 molecule of the two salts used jointly is -r rr- - A number 



.A. -f- _L> 



of experiments were made which showed that the actual con- 

 traction observed was sensibly identical (within experimental 



