Se oe Se 
W. J. Comstock—Tetrahedrite from Huallanca, Peru. 401 
So far as the salts used in these experiments are concerned, 
the theorem stands the test of experiment, and is demonstrated 
to be true. In explanation of the changes that occur when a 
hydrated salt is dissolved in pure water, it may be assumed 
that the salt is decomposed, separating into an anhydrous por- 
tion and saline water, the former going into solution and the 
latter uniting with the solvent water, increasing its volume. 
Yonkers, N. Y., Jan. 31st, 1879. 
at LIl.— Analysis of the Tetrahedrite from Huallanca, Peru ; 
by W. J. Comsrocx. Contributions from the Laboratory of 
the Sheffield Scientific School, No. LV. 
In this Journal for April, 1878, there is given a short extract 
from an article in the London Min ning Journal by Mr. Henry 
Sewell, F.R.G.S., describing the mineral caves of Huallanca, 
Peru. Mr. Sewell states that these silver- -producing _ are 
situated upon the eastern flank of the Peruvian Andes a 
altitude of 14,700 feet ae the sea, and 4000 feet aoe che 
town of Huallanca. The mass of the argentiferous ores consists 
of the mineral setrabeditas ‘these ores contain about 800 ounces 
much deep. Mr. Sewell describes the crystals as occurring in 
such abundance on the walls of these pies that ‘“ millions” of 
analyzed a portion of one of the “erytal and have obtained 
the idlawica results: Specific gravity =4 
i. IL. Mean. 
26°69 26°79 26°74 
Sb 9-08 9°04 9-06 
13°35 13°62 13°49 
Ag 3-95 3-77 3°86 
Cu 39°01 39°16 39°09 
Fe 5°46 et 5°46 
Zn 2°14 eee 2°14 
99°68 99°84 
I give below the amount of sulphur required to combine with 
each of the metals and also the atomic ratio. 
