18 
Records of the Geological Survey of India. 
we are dealing with masses very pure and very abundant, is not applicable to the sulphides of 
meteorites. Besides the fact that we can only operate upon very small quantities of Troilite, 
and can therefore in every case only obtain a very trilling deposit of sulphur, it must be re¬ 
membered that this mineral is very far from dissolving entirely in acids. It gives a 
residue, in which we find carbon in the form of graphite, small hyaline grains which have 
a composition very close to that of quartz, and small crystals which can he referred to various 
silicates. 
In the practical point of view’, therefore, we must seek for some reaction characteristic 
for one at least of the two sulphides in question. With this object I have submitted the 
protosulphide of iron and Pyrrhotine to a very large number of comparative trials. 
I shall not stop to show that the protosulphide precipitates metallic copper from its 
solution exactly as iron itself does, whilst the Pyrrhotine does not; the chemical reaction 
in virtue of which copper is so reduced offers some interesting peculiarities, and I have 
submitted these to a special stud}’. (1) Without anticipating the details, I may say that the 
protosulphide of iron obtained by the wet way gives rise to a metallic precipitation, as well 
as the same compound obtained in the dry way ; nevertheless the phenomenon is more easily 
perceived in the latter case, inasmuch as the extreme sub-division of the black sulphide 
leads the copper to deposit itself in grains not discernible by the eye, 
I have been able to replace the chemically pure protosulphide of iron by a compound 
containing a little more sulphur, produced by the preparation of sulphuretted hydrogen, 
in fusing together iron and sulphur. But as soon as the proportion of the sulphur approached 
that demanded by the formula of Pyrrhotine, precipitation ceased to be possible. 
With a sufficient quantity of protosulphide of iron, a copper solution can be deprived 
of all the copper it contains. This experiment can be easily made with a solution of the 
sulphate of the binoxide of copper; again, with a sufficient quantity of sulphate of copper, 
all the ii'on can he removed from the black precipitate which is obtained by the action of 
sulpho-hydrate of ammonia on an iron solution. 
These two facts show well that we have here to deal with a true chemical phenomenon, 
and not with a physical action due to capillarity or any other analogous cause. 
Having established this distinctive character so easily recognized between the proto- 
sulphide of iron and magnetic pyrites, I commenced a series of comparative trials on 
specimens of Troilite from different sources. All these specimens placed in the presence of 
solutions of sulphate of copper, of which I varied both the concentration and the temper¬ 
ature, proved absolutely inert. In this respect, therefore, as also in regard to its com¬ 
position, Troilite, according to my experiments, approaches closely to magnetic pyrites 
(Pyrrhotin e). 
It would doubtless be rash to conclude from this its absolute identity with Pyrrhotine, 
although that identity appears very probable. But the experiments appear to justify the 
absolute separation of Troilite from the protosulphide of iron, of which it possesses neither 
the composition nor character, as is easily proved. Cosmos, 18th January 1868.—T. O. 
(1) Cerlaiu phosphides of iron produce an analogous precipitation. 
