stokes.] ACTION OF CUPRIC SALTS. 43 
The solution therefore contains 55.3 per cent of the iron entirely as 
ferrous salt. The ferric oxide, extracted as above from the red-brown 
precipitate, was equivalent to 0.0225 gram iron. The final residue 
contained much iron. From these data it follows that 79.1 "per cent 
of the pyrite was decomposed, the dissolved portion giving — 
69.9 per cent ferrous iron. 
30.1 per cent ferric iron. 
Required by Brown's hypothesis, 20 per cent ferrous iron. 
EXPERIMENTS WITH CUPRIC SULPHATE AND MATtCASITE. 
Experiment Jf.. — MarcasiteNo. 10. Oxidation coefficient, 17.1. Time 
of heating, seven hours. 
Marcasite used . . 0. 2062 
Ferrous iron in solution . . 0559 
Total iron in solution . . ....... ... .0562 
Total iron in marcasite used . . . . 0901 
After extracting the red-brown precipitate, as above, the residual sul- 
phide was found to be free from iron, indicating complete decomposi- 
tion of the marcasite. From these data it follows that the marcasite 
yielded — 
58.2 per cent ferrous iron. 
41.8 per cent ferric iron. 
Required by Brown's hypothesis, LOO per cenl ferrous iron. 
Experiment 5. — Marcasite No. 10. Time of heating, fourteen hours. 
Marcasite used 0. 2096 
Ferrous iron in solution - . 0651 
Total iron in solution . . . . . Same. 
Ferric iron from precipitate . 0318 
Total iron in marcasite used _ . 0977 
The precipitate further yielded to hydrochloric acid 0.0620 gram cop- 
per, which was present either as cuprous oxide or as metallic copper, 
while the final residue was free from iron, showing that complete 
decomposition had been effected. The above data give for this 
experiment — 
66.6 per cent ferrous iron. 
33.4 per cent ferric iron. 
Required by Brown's hypothesis, 100 per cent ferrous iron. The cop- 
per sulphide remaining after extraction with hydrochloric acid con- 
tained 0.2300 gram copper, from which it follows that two atoms of 
copper are precipitated as sulphide for each atom of iron dissolved. 
This necessarily implies a reduction of the copper to the cuprous con- 
dition, and a corresponding oxidation of a portion of the ferrous salt 
or of the sulphur, or both. That cupric salts can accomplish both of 
these results is shown in the two following experiments. 
