IOWA ACADEMY OF SCIENCES. 
113 
reach an equilibrium in this reaction. To this end the fol- 
lowing series of determinations was made. As may be 
seen from the table the precipitation is most rapid about 
an hour after the beginning, then falls slightly and soon 
becomes nearly uniform. In general it may be said, that 
within the total period, the amount of precipitation is 
nearly proportional to the time, and at the end of seven 
and a half hours the reaction is yet far from a state of 
equilibrium. The result is plotted in curve “ M,” and 
from it one might easily infer that with sufficient time the 
precipitation of zinc even in this strength of acid might be 
complete. 
SKRIES II. 
NO, OF 
EXAMINATIONS. 
TIME— HOURS. 
ZN IN 
SOLUTION. 
FREE Hcl . 
1 
£ 
4.30 
2 
1 
3.84 
0.57 
3 
1£ 
3 47 
0 98 
4 
2 
3 00 
1 53 
5 
2£ 
2.78 
1.76 
6 
3 
2 63 
1 92 
7 
3£ 
2.48 
2.0« 
8 
4 
2.31 
2.27 
9 
4 £ 
2.25 
2.35 
10 
5 
2 13 
2.48 
11 
5£ 
1.98 
2 65 
12 
6 
1.92 
2 72 
13 
6£ 
1 81 
2.84 
14 
7 
1 69 
2.98 
15 
7£ 
1 55 
3.18 
Experiments were now undertaken to ascertain the 
influence of time alone. The results are given in the 
table below, in which X represents the time during which 
the gas was passed through the solution, and Y gives the 
time during which the solution was allowed to stand in 
contact with the precipitated zinc sulphide before it was 
filtered and the zinc determined. The results evidently 
point to a three-sided equilibrium between hydrogen 
sulphide, zinc chloride and hydrochloric acid: 
SERIES III. 
NO. OF 
EXAMINATIONS. 
X. 
M. 
ZN IN 
SOLUTION. 
FREE Hcl. 
i 
2 
18 
1.12 
3.62 
2 
1 
18 
2.40 
2.18 
3 
1 
42 
2 40 
2 17 
8 
