I IIKMICAL EXAMINATION OF MINERALS, ETC. 3 jf. 



ARTICLE XXIV. 



Chemical Examination of two Minerals from the neighbourhood of Reading, Pa. ; and on the 

 occurrence of Gold in Pennsylvania. By Charles M. Wetherili, Ph. l>. 



1. Molybdenite. — This mineral, specimens of which were given to me hy Dr. Bischoffand 

 (.( •(>. M. Keim, Esq., of Reading, is found in abundance at the Zion Church, Alsace, in 

 the neighbourhood of that city. It occurs of considerable purity in plates and Bcales 

 in a quartz matrix. The colour of the latter is like plumbago, but more brilliant. The 

 streak on paper, that of plumbago; on porcelain, olive green. It is impressible to 

 the nail, giving a hardness of 1 by Mobs' scale. 0-7255 grammes weighed in water, 

 0-565, corresponding to a density of 4*52. The following is its behaviour before the 

 blowpipe. Heated alone on charcoal, white fumes were evolved which coated the coal, 

 and the specimen was left tarnished. Heated alone in the open tube, sulphurous acid was 

 given off. In the platinum forceps, it coloured the outer flame yellowish green. On tin- 

 platinum wire in the outer flame, gave a glass, yellow ish when hot, colourless on cooling; in 

 the inner flame, the glass was greenish. Did not readily dissolve in this bead of micros- 

 comic salt. Borax gave similar reactions. Heated with nitre in the platinum Bpoon, 

 deflagrated with formation of sulphate and molybdate of potassa. Some of the crystalline 

 scales heated in the closed tube gave off a Bmall quantity of wat< r, the quantitative deter- 

 mination of which was effected l>\ raisins to a bright red beat in a covered crucible 0*673 

 grammes of the crushed mineral. The loss alter ignition was ()•()< )'_', corresponding to H 

 per ccntage of 0-297 water. A qualitative examination in the moist wa*j detected a- in- 

 gredients of the mineral, silica, sulphur, molybdenum and iron, the quantitative determina- 

 tion of which is afforded by the following analytical data. 0.2775 grammes of the mineral 

 (which was pulverized with great difficulty, on account of its soft and lamellar nature, 

 after several days 1 digestion in aqua regia, left a white residue of silica weighing 0*008, 

 corresponding to a per ccntage of 2-283. The sulphuric acid yielded on the addition ol 

 nitrate of baryta 0*7697, sulphate, which corresponds to 0*106, -ulpliur, or 38*198 per 

 cent. Alter removing the excess of baryta salt, the iron precipitated b) ammonia weighed 

 o-0<)!)7 or 3-195 per cent. It was proposed to determine the molybdenum as Mo bj 

 igniting the evaporated residue according to Rose, in an atmosphere of bydrogi I), but I tl 



