6 PHILOSOPHICAL TRANSACTIONS. [ANNO 17Q0. 



had passed, was found to be mixed with siliceous earth. When melted on charcoal, 

 it did not entirely assume the metallic form, but a part changed into a small grain 

 of transparent yellowish vitrified oxyde of lead. Mr. Klaproth observes, that in 

 this experiment the presence of the siliceous earth prevented the complete reduction 

 of the lead, in the same manner as when glass of lead, composed of 3 parts of 

 oxyde of lead and 1 of siliceous earth, is melted on charcoal. He therefore dissolved 

 this oxyde in weak nitric acid, separated the siliceous earth by a filter, and precipi- 

 tated the lead by sulphuric acid. Mr. Klaproth however, doubts whether the 

 greater part of the siliceous earth was not introduced, during the operation, by the 

 action of the alkali on the crucible. 



A drachm of the ore was digested with a considerable quantity of nitric acid, 

 and a great part was dissolved. In the solution white flocculi were perceived, and 

 were separated by a filter. When dried they were like a membrane, which became 

 bluish when exposed to the light, and much resembled the molybdic acid obtained 

 from molybdaena, by repeatedly distilling nitric acid from it. In the filtrated nitric 

 solution there was much oxyde of molybdaena mixed with oxyde of lead. The 

 lead was therefore precipitated by sulphuric acid, and afterwards the molybdaena by 

 prussiate of pot-ash. 



A drachm of the ore was digested with muriatic acid; and was completely dis- 

 solved, excepting a small residuum of siliceous earth. The solution was transpa- 

 rent, and without colour. In the course of some time it plentifully deposited crys- 

 tals of muriated lead. When these crystals were separated, the solution was evapo- 

 rated, and the interior of the basin was, during the evaporation, covered with a 

 bluish saline crust, which dissolved and the colour disappeared when the vessel was 

 shaken. The concentrated solution decanted from the muriate of lead, which had 

 been precipitated during the evaporation, was of a deep blue, which disappeared 

 when water was added. The solution was then saturated with alkali, and deposited 

 a white precipitate, which consisted of molybdic acid, together with a small quan- 

 tity of oxyde of lead. 



According to these experiments Mr. Klaproth remarks, that the yellow sparry 

 lead ore of Carinthia is composed of oxyde of lead and molybdic acid, and that this 

 mineralogical novelty is the more remarkable, as it is the only one of the kind 

 known at present. It is also worthy of notice, that the molybdaena changes its form 

 according to the method employed to precipitate it from alkaline solutions ; for 

 it is obtained either in a crystalline form, or in that of a white powder, or in that 

 of citron-coloured oxyde. When crystallized, it is soluble in acids, and in water; 

 as a white powder it does not dissolve in water, unless a small quantity of muriatic 

 acid be added ; but in the state of the citron-coloured oxyde, it is insoluble in wa- 

 ter as well as in the acids. Mr. Klaproth considers that this difference is occa- 

 sioned by the presence of some alkali in the first 2 substances, so as to form an 

 imperfect neutral salt with the molybdic acid, but that the yellow powder is in 

 the state of a simple oxyde. This yellow colour probably occasioned the suppo- 



