Dr. Genth’s Contributions to Mineralogy. 81 
Art. XI.—Contributions to Mineralogy; by Dr. F. A. Genta - 
of Philadelphia. 
1. Tetradymite.*—The uncertainty in regard to the chemical 
constitution of tetradymite renders it desirable, that this mineral 
should be re-analyzed in order to ascertain, whether it may be 
considered a tertellurid of bismuth, in w which a variable quantity 
of tellurium is substituted by sulphur, or a combination of one 
equivalent of tersulphid with two equivalents of tertellurid of 
bismuth. Several "years ago I discovered this rare mineral at a 
new locality, viz. een County, N. C., about five miles 
west of Wastin ati min 
It occurs there in foliated scales and lamellar masses of splend- 
ent metallic lustre, and between lead- and steel-color. H. =1-5; 
sp. gr. =7°237 (at 7° Cels. 
B.B. on charcoal it fuses readily, tinging the flame blue and 
giving off the odor of sulphurous acid and slightly that of selen- 
ium, leaving white incrustations with a yellow ring next to the 
substance. In an open tube it gives off white fumes and a sub- 
limate of tellurous acid. 
Only a few specimens came from this locality, and as they 
sin found near the surface, a great portion of the tetradymite 
s already oxydized. This ox ydized portion contains but a 
octal quantity of carbonate of bismuth ; the greater part seems to . 
e a combination of tellurous acid with teroxyd of bismuth, and, 
as it yields chlorine when dissolved in hydrochloric acid, some 
of the tellurium is oxydized into telluric acid. 
The accompanying minerals are gold, eonger pyrites, magnetic 
iron, brown hematite, epidote, quartz, ete. 
The substance for analysis was first fora with very diluted 
hydrochloric acid, in order to free it from the oxydized minerals, 
and then picked out. The pure scales were washed and dried. 
0-$039 grms. were dissolved in nitrohydrochloric acid, and the 
sulphuric acid formed in this manner precipitated by chlorid of 
barium ; the sulphate of baryta was filtered and first washed with 
diluted hydrochloric acid, finally with water. The dry sulphate 
of baryta was powerfully ignited, and after cooling, digested with 
diluted hydrochloric acid, filtered, washed and weighed. It was 
is precaution, though not generally in use, is of 
the greatest importance for a correct determination of ape 
acid (resp. sulphur) in all cases in which nitrie acid is in 
solution. It is well known, that in its presence a large a n 
of nitrate of wit: always falls down along with the sas ste of 
baryta. ‘This nitrate of baryta cannot be washed out completely, 
* An abstract of this —_ was published in Keller- Tiedenet Nordamerikanis- 
chen Monatsbericht, ii, 
Seconp Serres, Vol. st No, 46,—July, 1858. 1 
