THE DISSOCIATION OF DOUBLE SALTS 
499 
Concentration 
5 Per Cent 
FeS0 4 
(NHJoSO, 
Temperature 
Room Temp. 
Test No. 1 
.02548 
.05709 
Duration of Test 
' 3 Hours 
Test No. 2 
.01824 
.04244 
We find here an example of how the ammonium salt decreases 
at a more rapid rate than iron salt for the longer periods. 
Concentration 
5 Per Cent 
FeS0 4 
(NH 4 ) 2 S0 4 
Temperature 
Room Temp. 
Test No. 1 
.03998 
.07799 
Duration of Test 
5 Hours 
Test No. 2 
.04623 
.09438 
The ammonium sulphate is still on the ratio decrease and now 
for the five hour test it is less than twice the weight of the 
iron, while for the two hour period it was three times greater. 
Co n cen tr atio n 
5 Per Cent 
Temperature 
Room Temp. 
Test No. 1 
Duration of Test 
10 Hours 
Test No. 2 
FeS0 4 .08621 
(NH 4 ) 2 S0 4 .15411 
.09196 
.16478 
The total weight of the salts which came through the walls 
during the ten hour test is less than twice the weight of the 
salts which came through during the five hour test. This is 
another example of how the total amount of salt which passes 
through a dializer during any period of time, is greatest for 
the first period and decreases for each additional period. This 
is only to be expected for as the solutions within and without 
the porous cup come to approximate an equilibrium, there is 
less pressure and consequently less force to urge the salts 
through the membrane. 
GENERAL CONCLUSIONS FROM DATA SECURED. 
The double salts studied do not exist as such in aqueous solu- 
tions, but dissociate into simpler salts. 
The rate at which the dissociated ions of a salt pass through 
a porous membrane is inversely proportional to the size of the 
ions of that salt. 
Some ions, which are of themselves small, hydrate and thus 
become large and because of this they pass through the more 
slowly. This is in accordance with the “Hydrate Theory” of 
Jones and Knight. 
Department of Chemistry, 
Cornell College. 
