44 ON PYRITE AND MARCASITE. [bull. 186. 
EXPERIMENT WITH CUPRIC CHLORIDE AND PYRITE. 
Exp< riiii< a! 6. — 0.25 t5 gram pyrite was heated with 50 cm. ;! of a pure 
cupric chloride solution containing as much copper as the sulphate used 
in the foregoing experiments, the tube being filled with the usual 
precautions to prevent oxidation. The lube was heated five hours at 
200° and on cooling was found to contain undecomposed mineral and 
an abundant crystallization of cuprous chloride. The filtered solu- 
tion gave — 
0.0067 gram iron =0. 1429 gram pyrite. 
0.5540 gram BaSO 4 =0.1427 gram pyrite. 
It appears, therefore, that as far as it was decomposed the pyrite was 
completely oxidized to ferrous salt and sulphuric acid, with a cor- 
responding reduction of the copper from the cupric to the cuprous 
state, according to the equation 
FeS 2 +14CuCl 2 +8H 2 0=14CuCl+FeCl 2 +2H 2 S0 4 +12HCl. 
I have further obtained an abundance of sulphuric acid by oxidizing 
precipitated copper sulphide with cupric chloride solution at 100°, air 
being rigorously excluded. Doubtless in the above experiments with 
pyrite and marcasite and copper sulphate an analogous oxidation 
occurs, being obscured by other reactions. Chalcocite, however, is 
not perceptibly attacked by 10 per cent copper sulphate solution 
after fourteen hours' heating at 200°. 
EXPERIMENT WITH FERROUS AND CUPRIC SULPHATES. 
Experiment 7. — A mixture of equal volumes of 10 per cent solutions 
of crystallized copper sulphate and crystallized ferrous sulphate (care- 
fully freed from ferric salt by reduction with hydrogen sulphide) was 
heated, under absolute exclusion of air, for three hours at 200°. A 
considerable red precipitate was obtained, which consisted of a mix- 
ture of ferric oxide or basic sulphate with cuprous oxide and appar- 
ently metallic copper. The reduction of cupric by ferrous salts in 
neutral or acid solution is frequently referred to in the literature, but, 
so far as I can ascertain, without experimental basis. 
Theory of the reaction. — The explanation of the result is probably 
the following: In the mixture we have equilibrium between the cupric, 
cuprous, ferrous, and ferric ions and copper, as represented by the 
equations 
Cu"+Fe"£Cu'+Fe" 
Cu"+2Fe "£Cu+2Fe" 
in which but traces of Cu, On', and IV" exist. 1 On heating the trace 
of ferric salt is precipitated in the basic form, the equilibrium is dis- 
1 The slight solubility of cuprous compounds shows that not more than traces can be present. 
