42 ON PYRITE AND MAROASITE. [uttix. 186. 
freed from air by boiling out and cooling in carbon dioxide. The 
lubes were filled with carbon dioxide, carefully sealed in a current of 
the same gas, and heated for varying times at 200° C. The filtration 
and titration with permanganate of the resulting solution were also 
made in an atmosphere of carbon dioxide, and the end-reaction, 
which is not very sharp, was determined b} 7 comparison with a copper 
sulphate solution of about the same strength. 
EXPERIMENTS WITH CUPRIC SULPHATE AND PYRITE. 
Experiment i.— Pyrite No. 4. Oxidation coefficient, 60.3. Time of 
heating, ten hours. 
Pyrite taken 0. 2024 
Ferrous iron in solution . _ . 0305 
Total iron in solution __ ._.. 0314 
Total iron in pyrite used 0944 
The solution therefore contains 33.3 per cent of the iron, practically 
all in the ferrous condition, against 20 per cent as required by Brown's 
hypothesis. The precipitate was red-brown. In a separate experi- 
ment the red substance was found to be left behind on oxidizing the 
sulphide with dilute nitric acid, and proved to be ferric oxide or a 
very basic sulphate. It is easily soluble in hot dilute hydrochloric 
acid, and can thus be separated from the sulphide and determined. 
Experiment 2. — Pyrite No. 5. Oxidation coefficient, 00.8. Time of 
heating, eleven hours. 
Pyrite taken. 2028 
Ferrous iron in solution .. _ . 0510 
Total iron in solution Same. 
Total iron in pyrite used _ . 0946 
The solution contains 53.9 per cent of the iron, all in the ferrous 
state. The ferric oxide in the red -brown precipitate was extracted 
by boiling ten minutes with dilute hydrochloric acid in a current of 
carbon dioxide, whereby some copper also dissolved. The ferric iron 
thus determined was 0.0272 gram. The final residue, oxidized with 
aqua regia, gave much iron, which must have come from undecom- 
posed (or imperfectly decomposed) pyrite. From the sum of the two 
irons above determined it appears that 82.7 per cent of the pyrite was 
decomposed, and that this portion gave — 
62.5 per cent ferrous iron. 
34.8 per cent ferric iron. 
Required by Brown's hypothesis, 20 per cent ferrous iron. 
Experiments. — Pyrite No. 5. Time of heating, seven hours. 
Pyrite used.. . 0.2027 
Ferrous iron in solution . . . 0527 
Total iron in solution ... . 0523 
Total iron in pyrite used ... ..;. .0945 
