URANIUM, a foil found at Johangeorgenſtad in Saxony, and at Joachimſtal in Bohemia, and is, by the miners, called Pechblend. M. Werner, a German mineralogit, being convinced that it was not a blend, gave it the name of Ferrum Othraceum Piceum, and thought it contained the tungſtic acid combined with iron: but M. Klaproth is of a contrary opinion, and maintains that it is very different from wolfram. There are (he ſays) two varieties of pechblend: the one is of a dark grey colour, with very little brilliancy, the particles of which have the form of a flattened conchoid; it is not very hard, and, when triturated, becomes a black powder: its mean ſpecific gravity is 7.5. The other is diſtinguiſhed by its black colour, though it ſometimes assumes a reddiſh tint: its ſurface is more brilliant than that of the former, and reſembles pit-coal; it is alſo leſs hard; and the black powder, to which it is reduced by trituration, has a greeniſh hue. This kind is generally diſcovered in compact maſſes, lying between ſtrata of a micaceous ſchiſt, which is found to be decompoſed. In the internal parts of this ſtone, it is not uncommon to meet with veins of a peculiar yellow metallic earth. The pechblend is
ſoluble in the nitric and in the nitro-muriatic acids, partially ſo in the muriatic, but not at all in the ſulphuric. From theſe ſolutions, the unfaturated ferruginous pruiſſat of potaſh, or phlogiſticated alkali, precipitates the metallic ſubſtance, which then reſembles kermes mineral in colour. This, when it does not unite in flakes, but is uniformly diffuſed in the ſolution, may be conſidered as one of the moſt diſtinguiſhing characters of the pechblend; another is, that the precipitates, effected by the volatile and fixed alkalis, are yellow; the fixed cauſtic alkalis giving it a lemon colour, the aerated a like yellow. This yellow oxyd, or calx, cannot be fuſed with alkalis. As this foil cannot be claſſed either among the zinc or iron ores, and is very different from tungſtein, M. Klaproth propoſes to give to it the appellation of Uranium; and he diſtributes it into the following ſpecies: