THE DISSOCIATION OF DOUBLE SALTS 
493 
With this assurance that we had the right salt we proceeded 
with the diffusion tests using the method outlined in the fore- 
going. We made these tests at several temperatures and also at 
different concentrations and time intervals. 
Concentration Temperature Duration of Test 
5 Per Cent 13°C 45 Minutes 
We found on the analysis of the diffusate, the following 
amounts of the salts in solution: (Weight in grams.) 
Test No. 1 Test No. 2 
CdBr 2 .04009 .04131 
NaBr .02290 .02320 
In the double salt crystals, the proportional parts of the 
various elements may be represented by the formula : 2NaBr. 
3CdBr 2 . Since the molecular weights of these are 206 and 
810 respectively, it is evident that, if this salt does not dis- 
sociate in a water solution, the two salts found in the diffusate 
will bear the same ratio to each other. Prom the above mole- 
cular weights it is seen that the cadmium bromide should be 3.9 
times heavier than the sodium bromide, if the double salt has 
not dissociated. We find from the analysis of the diffusate that 
the sodium bromide is a little more than half the weight of the 
cadmium bromide that diffused through the walls of the porous 
cup. 
Concentration 
5 Per Cent 
CdBr 2 
NaBr 
Temperature 
46°C 
Test No. 1 
.10045 
.04953 
Duration of Test 
45 Minutes 
Test No. 2 
.10915 
.05244 
In this we have less than half as much of the sodium bromide 
as of the cadmium bromide. It seems that less of the salt 
has dissociated since the ratio is more nearly 1 to 3.9. This 
may not necessarily point to the fact that the salts break down 
more easily in cold than in warm water. It may be that the 
heat has so lessened the internal friction of the solvent that it 
passes through the walls more easily and in carrying a larger 
amount of the salt through in the same time, the more cadmium 
bromide is taken through. This is only a supposition, however. 
