1871.] Dr. A. Schrauf on Molybdates and Vanadates of Lead. 457 



could not detach any particle of the small group of crystals at my disposal 

 for the purpose of chemical investigation, being thus obliged to confine 

 it to two varieties of vanadinite from Kappel, and to a specimen of de- 

 chenite. On two specimens of vanadinite from Kappel, vanadinite appears 

 in the form of crystals intimately connected into a crust, the single crystals 

 not exceeding the size of §-§ millim. On one specimen (variety A), the 

 greater number of the larger crystals is of a dark greenish-brown colour 

 (fluorescence-colour?), and without translucidity ; the smaller ones are 

 reddish brown and translucid ; the streak is brownish orange. This 

 variety agrees, in all its external characters, with the specimen of Peruvian 

 descloizite now before me ; the crystals of it are reddish to greenish brown, 

 translucid, and their streak is brownish orange*. 



The crystals of the second specimen (variety B) form a thin crust over 

 limestone ; they are |-1 rnillim. in size, rather translucid, of lighter 

 carnation tint, and less bright than those of variety A. The crystals of 

 variety A show a vivid metallic brightness, while the light carnation ones 

 of variety B scarcely offer a faint vitreous brightness, very easily altered 

 by contact with moist air ; even the moisture contained in the breath 

 is sufficient to produce a superficial decomposition of the crystals of 

 variety B. Their brightness is immediately tarnished, and in a few 

 minutes very diminutive greyish-white globules cover, like Mucedinese, 

 the surface of the crystal. Some time after, these globules assume a 

 slight yellowish colour, but spread no further over the specimen if it is 

 kept in dry air. The supposition of this alteration being caused by 

 the presence of arsenic is contradicted by the results of subsequent 

 investigation ; proving arsenic, if it exists at all, to exist in such dimi- 

 nutive proportion that visible marks of its presence could not be obtained 

 by heating the mineral on charcoal or in a glass tubef. Notwithstand- 

 ing' the differences detailed above the actions of hydrochloric acid, of 

 alcohol, and of bisulphate of potash give evidence of the notable difference 

 between eosite, descloizite, and vanadinite, and of the nearly absolute identity 

 of the two varieties of vanadinite from Kappel. 



Small splinters of both these varieties, moistened with hydrochloric acid 

 on a glass plate, become yellowish grey on their margins, the internal 

 portion assuming a dark reddish-brown tint. Under the protracted 

 action of the acid this nucleus becomes darker and lessens in size, till at 

 last it disappears, leaving a portion of uniformly greyish-white substance. 

 The nucleus of the carnation variety B shows a somewhat lighter tint 

 at first; this difference, however, vanishes more and more under the 

 lengthened action of acid ; alcohol added to the cold solution of both 

 varieties causes the separation of a yellowish-green gelatinous substance, 



* See Schrauf "On the identity of vanadinite and descloizite" in Poggend. Ann. 

 vol. cxvi. (1861). 



t Several experiments intended for ascertaining directly the chemical character of 

 these efflorescences remained without any satisfactory result. 



2 n 2 



