496 
IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
This test also shows a larger proportion of the ammonium 
bromide. The raising from “Room Temperature” to 55° C. 
has also been an active agent of dissociation. 
Concentration 
5 Per Cent 
ZnBr, 
NHJBr 
Temperature 
55 °C 
Test No. 1 
.02518 
.08336 
Duration of Test 
15 Minutes 
Test No. 2 
.01972 
.08059 
The data here recorded in connection with the preceding tests, 
give an excellent example which shows how the amount of solid 
matter that diffuses through the cup per unit of time, is greatest 
for the first unit of time. and becomes smaller and smaller as 
the solutions become more nearly in an equilibrium. It is noted 
that half as much of the zinc bromide was diffused in the first 
fifteen minutes as was diffused during the full hour test. This 
rate of decrease for each succeeding period diminishes until with 
long duration of time tests, when the solutions become nearly 
saturated, the difference or the rate of decrease is very small. 
C O N CENTR ATION 
5 Per Cent 
ZnBr 
NH 4 Br 
Temperature 
Room Temp. 
Test No. 1 
.27178 
.80585 
Duration of Test 
12 Hours 
Test No. 2 
.33168 
.832206 
This test was made under the same condition as one of the 
foregoing and similar results were obtained, each serving to 
check the other. 
Concentration 
5 Per Cent 
ZnBr 2 
NHJBr 
Temperature 
Room Temp. 
Test No. 1 
.12064 
.46180 
Duration of Test 
6 Hours 
Test No. 2 
.10240 
.47242 
It may be noted when comparing this six hour test with the 
twelve hour tests, that less than half as much of the zinc bro- 
mide was diffused, while more than half as much of the am- 
monium came through the walls. 
Conclusions — (1) Zinc ammonium bromide dissociates in water 
solution. (2) Ammonium bromide passes through a membrane 
faster than ZnBr 2 . (3) Ammonium bromide dializes much 
faster than ZnBr 2 at the beginning of the test, but the amount 
dialized, per unit time, decreases more rapidly when the time 
is lengthened. 
