380 Plumbago in Coal- Gas Retorts, «^c. 



13. Plumbago m coal-gas Retorts. — The following de- 

 scription of an artificial plumbago, is by the Rev. J. J. Co- 

 nybeare ; he is speaking of the retorts in the Bath gas- 

 works. The unserviceable retorts, on being withdrawn 

 from their beds, are found lined with a coating of plumba- 

 go averaging the thickness of four inches. This coating is 

 thickest towards the bottom of the retort. The general 

 aspect of the predominant variety may be thus described : 

 colour, iron-grey, somewhat lighter than that of native plum- 

 bago ; texture scaly ; structure mammellated, usually in ve- 

 ry close aggregation— some specimens exhibit this structure 

 on the large scale, but generally it requires the lens, to be 

 seen ; hardness variable, but always greater than the best 

 native plumbago — scratches gypsum, but is scratched by 

 calc. spar ; lustre of the fracture usually but small ; lustre of 

 the exterior surface sometimes very considerable ; the 

 pawder uniformly resembles that of common plumbago, 

 but is somewhat less brilliant. The quantity of iron in it 

 seldom appeared to amount to 9 per cent. It is hardly fit 

 for the finer purposes of art, but it is proposed to use it in 

 diminishing friction, in making crucibles, furnaces, &;c. 

 Ann. Phil. v. 5 1 . 



14. Analysis of Uranite. — R. Philips has lately reanaly- 

 zed this mineral and very unexpectedly finds it to contain 

 phosphoric acid ; indeed, to be a phosphate. A specimen 

 from Cornwall gave, 



Silicia - - - - - 0.5 



Phosphoric acid, - - - - 16.0 



Oxide of Uranium, .• - - 60. 



Oxide of Copper, . - - - 9.0 



Water, - ... - 14.5 



100. 



or, neglecting the Silicia, 



Phosphate of Uranium, - - - 73.2 

 Phosphate of Copper, - - - - 12.3 

 Water, - - - - . - 14.5 



Ann, Phil. v. 59. 



