422 Dr. Schaf haeutl on the Different Species of 



est part of the remaining finely divided, and therefore, ex- 

 tremely light silica. 



Nitrate of potash is likewise not to be recommended for de- 

 composing plumbago, as the deflagration is so violent, that not 

 only much of the mass is liable to be lost, but a great deal of 

 it remains iindecomposed ; and the silver crucible very fre- 

 quently melts. I found carbonate of ]iotash or soda decom- 

 posing plumbago quietly and perfectly, even in a dull red 

 heat. If a white heat be used, the evolution of carbonic acid 

 gas is very violent ; so much so, that drops of the liquid mass 

 are thrown up against the lid of the crucible, and the crucible 

 itself is very much attacked. In order to ascertain the vola- 

 tile parts of plumbago, it must be mixed with chromate of 

 lead and chlorate of potassa in a glass tube heated over a coal 

 fire, and the gas collected after the well-known methods of 

 Berzelius and Liebig. 



Before ascertaining the proximate chemical components of 

 black lead, I digested the well-washed and cleansed material in 

 nitromuriatic acid for several days in a sand batii ; the solution 

 was then separated from the black lead, evaporated to dry- 

 ness, afterwards dissolved in hydrochloric acid, the remaining 

 silica collected on a filter, and the oxide of iron thrown down 

 by ammonia ; the well-washed residuum of black lead was 

 then, still wet, heated with a strong lye of caustic potash, or 

 better, soda, the filtered lye neutralized with hydrochloric 

 acid, evaporated to dryness, and the silica separated in the 

 well-known manner. 



Graphite (a) in paper-like leaves or scales, appeared after 

 this treatment to have perhaps increased slightly in bright- 

 ness, but graphite (b) remained quite unaltered in its appear- 

 ance. The graphite, freed in this manner from its mechani- 

 cal admixtures, was then mixed with five times its weight of 

 carbonate of soda, and kept for half an hour in a bright red 

 heat; and after the crucible had been allowed to cool, the 

 alkaline mass was found perfectly fused, with a dirty yellowish 

 brown centre, when graphite [a) had been used, but perfectly 

 white when graphite {b) was subjected to the same process. 

 The chemical composition of [h) was by this method found to 

 be in 100 parts 



(«.) Substances soluble in acids and alkalies. 



Protoxide of iron *... 18'60 



Silica 7-62 



26-22 

 Very nearly resembling the formula P S. 



