VOL. LXXXVI.] PHILOSOPHICAL TRANSACTIONS. 7 



sition that the lead was mineralized by the tungstic acid ; but the blow-pipe is suffi- 

 cient to distinguish them. The yellow oxyde of molybdaena loses the colour as 

 soon as the point of the flame touches it, inclines to an olive colour, and melts into 

 small grains, which are immediately absorbed by the charcoal. In the phosphate of 

 ammonia and soda it dissolves, and communicates to it a green colour. On the 

 contrary, the yellow oxyde of tungsten by ignition becomes blue or black, remain- 

 ing refractory, and with phosphate of ammonia and soda it produces a sky-blue 

 glass. 



Mr. Klaproth concludes his paper by saying, that he could not exactly determine 

 the proportions of the ingredients, as the quantity of the ore in his possession was 

 not sufficient to make the necessary allowance for the solubility of the oxyde of lead 

 in the alkalis, and especially that of the molybdic acid when in a state of combination. 

 These experiments of Mr. Klaproth, certainly prove that this ore is a molybdate of 

 lead ; but as the quantity which he had was too small, either to make a greater 

 number of experiments, or a regular analysis, I was induced to attempt a further 

 investigation of it ; and therefore in the course of the last summer I made the 

 experiments and analysis which are described in this paper. 



§ 1. Characters of the Carinthian Molybdate of Lead. — The molybdate of lead 

 is found at Villach, in Carinthia *. The matrix is a lime-stone, of a pale brown- 

 ish-grey colour, often more or less tinged with oxyde of iron. The ore is a heavy 

 brittle substance, easily scratched with a knife, and of a yellow colour, varying from 

 pale yellow to orange. The fracture is sparry. 



The external lustre is like that of wax ; and when crystallized, 2 of the faces of 

 the crystals are commonly opaque, and of a pale yellow, but the remaining 4 faces 

 or sides have a resinous appearance. It generally exhibits an appearance of crystal- 

 lization, and the crystals, when perfect, afford various modifications between the 

 octoedral figure and the cube. 



The specific gravity of a specimen, from which I had separated all the visible 

 part of the matrix, was 5092, the temperature of the water being 60°, but when 

 the ore was reduced to powder, and purified by diluted nitric acid, I found the spe- 

 cific gravity to be 5706. 1. When the ore was examined by the blow-pipe, it at 

 first split and crackled as soon as the point of the flame touched it, but afterwards 

 readily melted into a dark-coloured mass, in which were some shining globules of 

 lead. 1. With borax it formed a brownish-yellow globule ; but when it was in a 

 small proportion, and heated by the interior flame, it occasionally produced a glass, 

 which was greenish blue, and sometimes deep blue. 3. With phosphate of 

 ammonia and soda it formed a sea-green glass, which in proportion to the quantity 

 of the ore sometimes became deeper in colour, so as to be nearly of a deep blue. 



Before making the following experiments, I reduced 8 oz. of the ore to a fine 

 powder, and dissolved the matrix after the manner of Klaproth, by successively 



* It is said to have been sometimes found in Austria and Hungary, but I doubt if the nature of these 

 ores is the same.— Orig. 



