IOWA ACADEMY OF SCIENCES. 
115 
SERIES VI. 
NO. OF 
TIME. 
ZN REMAINING IN 
EXAMINATIONS. 
TEMPERATURE. 
SOLUTION. 
l 
20 w 
5 hours 
1.41 
2 
50° 
5 hours. 
1.49 
It is evident that a difference of 80° causes very little 
difference in the rate of precipitation, and probably the 
point of equilibrium is only very slightly shifted by change 
in temperature, but the latter point has not yet been 
determined. 
A solution of zinc sulphate was next used, in order to 
determine the part played by the acid. The method 
employed was essentially the same as that previously 
described, namely, fractional . precipitation and the deter- 
mination of the zinc and free acid in the several frac- 
tions. The rate of the gas was, as before, about four liters 
per hour. It will be observed that the precipitation is 
practically complete at the end of seven hours, even 
though 4.47 per cent of free sulphuric acid was present. 
In general the curve closely resembles that of the chloride. 
SERIES VII. 
NO. OF 
EXAMINATIONS 
TIME 
ZN REMAINING IN 
SOLUTION. 
FREE H2 SO4. 
1 
n 
1.60 
2.12 
2 
2 
1.25 
2 65 
3 
3 
.75 
3 40 
4 
4 
.38 
3.95 
5 
5 
.18 
4.26 
6 
6 
.07 
4.38 
7 
7 
.03 
4.47 
In order to find the point of equilibrium, if possible, a 
solution containing more acid was used. As may be 
observed in Series VIII, precipitation was still going on at 
the end of ten and a half hours when there was 5.25 per 
cent of free acid in the solution. The results are shown 
graphically in curve Y. 
