34 Analysis of Tin Pyrites. 
Cornwall, and which, on examination, proves to be tin pyrites, — 
d. 
and apparently in a purer state than any hitherto analyze 
his specimen occurs in quartz which has obviously been — 
taken from a vein in granite. The structure appears to be crys- 
talline, although no distinct planes could be observed. The color 
1s not steel-gray, as in that of the mineral from Wheal Rock, but 
iron-black, with slight superficial blue and red tarnish in some 
places. Streak black, lustre sub-metallic, fracture uneven. Hard- 
ness =4, Sp. gr. =4:522. Heated before the blowpipe, on 
charcoal, sulphurous acid is given off, oxyd of tin deposited in 
large quantity upon the charcoal, and a black globule obtained, 
from which copper and tin may be reduced on the addition of © 
a. 
A carefully conducted quantitative analysis, in which chlorine 
was used to decompose the mineral, gave the following results. 
Equivalents. 
a 
Supheg a eee ee eae ee 
Tin, : S - 26°85 ‘ é 4 > 455 2° 
Copper, See vip BPs ee. Misr eles, ‘920. 4044 
Tron, : . : 6°73 *240 a: 
Zinc, . . * 7:26 994. t ¥ a 464 2 040 
Gangue, 2 16 
99°64 
Thus the relative number of atoms of sulphur, tin, copper, and 
iron and zinc, as given in the 2nd and 3rd columns above, are 
almost exactly as 8: 2: 4: 2; whence we have the formula first 
assigned by Kudernatsch, (Pogg. Ann., xxxix, 146,) viz., 2(Fe 
S+ ZnS), Sn82+2CueS, SnS:. The present analysis agrees 
so closely with this formula, from which the results of Kuder- 
natsch, and even those of Rammelsberg, (Handw. d. Chem. 
Theils d. Mineral. 2d Suppl., 179,) sensibly differ, that it seems — 
fairly to be considered as representing the composition of the — 
mineral in a pure state. The analysis also possesses some interest 
in showing the presence of zinc in considerable quantity, therein — 
agreeing with Rammelsberg’s analysis above referred to of the mil- 
eral from Zinnwald. It is to be observed that in both cases the irol 
and zinc occur in very nearly atomic proportions, so that perhaps 
the formula should be written 2FeS, SuS:+2ZnS, SnS- +2(2 
u:S, SnS:), though this does not seem very probable, sincé 
Kudernatsch found 12-44 p. ct. of iron to but 1°77 of zinc, while 
Johnston gives 10-113 p.c. of the latter to 4-791 of the former, 
as contained in tin pyrites (from the same locality as the specimen 
submitted to the present avalysis, St. Michael’s Mount). The 
presence of this large quantity of zinc, is however of importance, 
chiefly as proving that the tin must enter into the composition 0 
the mineral as bi-sulphuret, since the other formula which bas 
been proposed, namely, 2SnS, FeS2+2Cu.S, FeS:, woul? 
