1874.] jizd [Q-entit, 



with rubber, will resist the action of standard acids, and shows no sign 

 of oxydation and dissolution. The rubber coating is done very quickly 

 with a concentrated chloroformic solution. The dipping in and drying is 

 repeated several times. I have fui-nished now all the burettes used by 

 my students with this simpler contrivance ($1.00) and have found my ex- 

 pectations more than realized. The surface of contact between the rub- 

 ber and the standard solutions is so small, that a deteriorating influence 

 on the latter could not be noticed. 



I must acknowledge my obligation to Mr. J. Zentmayer, the well- 

 known optician and mechanician, of this city, for the practical execution 

 of my ideas and for many valuable suggestions in the course of my ex- 

 periments. Any further information that may be deemed necessary shall 

 most gladly be given. 



CONTRIBUTIONS FROM THE LABORATORY OF THE UNIVER- 

 SITY OF PENNSYLVANIA. 



No. III. 



ON AMERICAN TELLURIUM AND BISMUTH MINERALS. 



By F. A. Genth. 



{Bead before the American Philosophical Society, August 21si, 1874.) 



On several occasions I have given descriptions and analyses of tellurium 

 minerals, which have been found associated with the gold ores of this 

 country. Since my last paper on this subject (Amer. Journ. of Science 

 [2] XL v., 306-319) several highly interesting discoveries have been 

 made, which not only augment the list of species, but also corroborate 

 some of my former observations. 



Most important is the occurrence of the tellurium ores at the Red 

 Clou^d Mine, near Goldhill, in Boulder County, Colorado. Prof. B. Sil- 

 liman (Journ, of Science [3] VIII. 25-33), has given a very accurate and 

 careful description of some of the minerals found at this locality, and 

 au exceedingly interesting account of the geological position of the vein. 



Through the liberality of my friend J. F. L. Schirmer, Esq., Super- 

 intendent of the United States Mint at Denver, Colorado, I have been 

 put in possession of a considerable quantity of very pure and excellent 

 material for investigation, including several varieties not mentioned by 

 Prof. Silliman. 



Another interesting locality of tellurium minerals is the Briggs or 

 King's Mountain Gold Mine, sometimes called the Gaston Mine, in Gaston 

 Co., N. C, where I noted this occurrence about two years ago. 



A third one is in the neighborhood of Highland, Montana. Several 

 others of minor importance will be mentioned under the different species. 



The following are the results of my investigations : 



