18 
ON PYRITE AND MARCASITE. 
[BULl, 186. 
either to weigh the material or to measure the liquid accurately, but 
in order to make unavoidable experimental errors as nearly as possi- 
ble constant, it is desirable always to employ approximately equal 
quantities, and to boil for nearly equal times. 
INFLUENCE OF CONCENTRATION. 
Since the equation expressing the oxidation of the sulphur is of a 
higher order than that denoting the oxidation of the iron, it follows 
that the rate of oxidation of the sulphur must fall off more rapidly 
than that of the iron, with decreasing concentration of the ferric salt; 
hence the value of p must constantly decrease as reduction proceeds, 
and comparable results can be obtained only by carrjung the reduc- 
tion to completion. This is shown in the following cases, where the 
experiment was stopped after p>artial reduction : 
Results of experiments showing constantly decreasing value ofp as redaction 
proceeds. 
Pyrite. 
Marcasite. 
Fe reduced. 
p' 
Fe reduced. 
V 
Per cent. 
Per cent. 
Per cent. 
Per cent. 
67.8 
71.4 
69.2 
23. 3 
88.7 
65. 2 
78.5 
22. 5 
90.5 
64.9 
100.0 
16.2 
95.2 
63.2 
99.5 
61.5 
100.0 
60.4 
1 
INFLUENCE OF TEMPERATURE. 
The influence of temperature on p is shown by the following experi- 
ments at 20° and at boiling temperature, the reduction being com- 
plete in each case: 
Results of experiments showing influence of temperature on p. 
Pyrite. 
Marcasite 
