120 Prof. Chapman's Mineralogical Notes. 



4. Tungstate of Lead : — Scheeletine. — Amongst some tabular 

 crystals of molybdate of lead, on a specimen from Coquimbo (?) 

 in Chile, I observed several elongated and slightly curved forms, 

 which at first sight I took to be tungstate of lime. On exposing 

 a particle, however, to the action of the blowpipe, the flame 

 assumed the peculiar blue colour indicative of the presence of 

 lead, but without the accompanying green tint at the point and 

 sides, which is always produced by the molybdate. On charcoal, 

 with soda, globules of lead were obtained j and a more extended 

 examination showed the presence of tungstic acid, oxide of lead, 

 and lime. The general configuration of the crystals is exhibited 

 in the annexed drawing. A : A over a middle Yie. 8. 



edge = 114° 32'; 0:0 = 131° to 131° 30*. 

 The latter angle could only be approximately 

 measured, owing to the unfavourable con- 

 dition of the faces. Calculation shows that 

 it should equal 131° 6 ; . The cleavage seemed 

 parallel to the position of the basal planes P 

 (OP of Naumann), and the points of many of 

 the crystals were thus broken off. Colour 

 pale yellowish-gray ; H.30; spec. grav. 7*87. 



17*26 grs. yielded on analysis: — tungstic 

 acid, 10*27; oxide of lead, 5*74; lime, 1*10; 

 corresponding to the per-centage composition. 



Tungstic acid . . . 59*50 

 Oxide of lead . . . 33*26 

 Lime 6*37 



9913 



These values lead to the common formula (PbO, CaO), WO 3 , 

 in which a portion of the oxide of lead is replaced by lime. 



In another trial, 12*85 grs. of the mineral gave 7*69 grs. of 

 tungstic acid, or 59*84 per cent. 



The mineral in a very fine state of subdivision was decomposed 

 by fusion with five parts of carbonate of soda and one part of 

 borax. The alkaline tungstate thus formed was dissolved in 

 water, and the residue well washed with water containing a little 

 ammonia. In several preliminary trials it was found that not a 

 trace of tungstic acid was left in the residue after this treatment. 

 Owing probably to the presence of tungstate of lime in the 

 mineral, the decomposition was also found to be much facilitated 

 by the addition of the borax. The tungstic acid was precipitated 

 by nitric acid, redissolved in ammonia, which left a trace of 

 silica, and again thrown down by nitric acid. The residue of 

 the first treatment was dissolved in diluted nitric acid, the lead 

 thrown down as sulphide, and the precipitate converted into 

 sulphate. The lime was also weighed as sulphate. 



