82 Dr. Genth’s Contributions to Mineralogy. 
not even with boiling water; the best mode to get such sulphate 
of baryta pure is to decompose the nitrate of baryta by heat, 
and to extract the caustic baryta afterwards with diluted hydro- 
chloric acid. : 
After freeing the filtrate from the excess of chlorid of barium 
by sulphuric acid, the solution was treated with hydrosulphuric 
acid, and from the precipitate thus obtained, tellurium was sepa- 
rated by digestion with sulphid of ammonium. The filtrate — 
containing it, was evaporated nearly to dryness and oxydized 
with nitrohydrochloric acid, the nitric acid removed by evapora- 
tion with an excess of hydrochloric acid and the tellurium then 
precipitated by bisulphite of ammonia. This metal filtered upon 
nown weight was found to be 0°3000 grs. 
The precipitate of tersulphid of bismuth was dissolved in 
00115 grs. The iron being an impurity in tetradymite was cal- 
culated as iron pyrites and subtracted from the original weight. 
Thus the analysis gives as the composition of this tetradymite : 
Bi 61351 Te 33-837 Se trace S 5270=100.458 
61351 83837 5270 j 
307-996 ° 64141 * 160G0 = 295 : 0528 : 0:308 
This ratio does not very well correspond with the formula 
BiSs+2Bi Tes, for which the calculated per-centage would be: 
Bi 59-033 Te 36-409 S 4558 
The analyses of the tetradymite from Schubkau in Hungary, 
by Berzelius and Wehrle, and that of the same mineral from 
Whitehall in Virginia by C. T. Jackson, (the latter after subtrac- 
tion of gold, &c.) give: 
: Berzelius. Wehrle. C. T. Jackson. 
Bi - 58°30 60:0 “BL 
Te - 36:05 84-6 35°95 
5 . 4°32 48 374 
99-4 100-00 
It will be seen, that Berzelius’s analysis accords better with the 
above formula than that of Wehrle, and that mine is very similar 
to the latter. 
I will now compare these analyses with the formula Bi (Te,S)s, 
considering the quantity of tellurium as correct. After calcu 
lating for it the requisite quantity of bismuth to form Bi'Tes, 
I take the difference as BiSs and get in this manner the follow- 
ing per-centages : 
Genth. Wehrie. i 
Bs. 60-7. oor ‘suas. 
Te - 83°34 84°6 36°05 35°95 
Ss - 497 4-4 3°88 4°72 
