334 M. Karsten's Observations and Experiments 



m 



increases, then the coals which are very rich in carbon often 

 present a much less specific gravity than the combustibles in 

 which the proportion of carbon is small. It may be admitted 

 as a general rule, that the proportion of carbon being the same, 

 the mineral combustibles which have the smallest specific gra- 

 vity, are always those in which the relation of the oxygen to 

 the hydrogen is the smallest that it can be. 



M. Karsten proceeds next to an examination of glance-coal, an- 

 thracite, and graphite. 



The author thinks that the combustibles known by the name 

 of glance-coal, whether of Schcenfeld or of Lischwitz in Saxony, 

 or of Vise near Liege, are nothing else than a coal which con- 

 tains a very large proportion of carbon. He is led to suppose 

 that graphite and true glance-coal, that of Rhode Island, for 

 example, were originally substances analogous to coal ; but that, 

 in these substances, the separation of the constituent parts of 

 coal is so advanced, that, at the present day, they have almost 

 all attained the state of pure carbon. From the experiments 

 which M. Karsten has made with reference to this subject, he 

 concludes, that native graphite is erroneously considered as a 

 carburet of iron, and that this substance should not be con- 

 founded with the graphite which is artificially obtained in fur- 

 naces. This latter substance, says the author, comes much 

 nearer to glance-coal in its lustre, its hardness, and its resistance 

 to combustion, than to native graphite. The two kinds of gra- 

 phite have only perhaps been confounded together, because 

 they both have the property of staining the fingers. Perhaps 

 the graphite of high furnaces, from the strength of its lustre, 

 and the difficulty of its combustion, presents a transition from 

 glance-coal and native graphite to diamond. 



According to the author's researches, the native graphite of 

 Borrowdale in England contains at the most 15 per cent, of 

 foreign parts, which consist of silica, alumina, oxide of iron, 

 oxide of manganese, magnesia, and oxide of titanium, with a 

 trace of chrome and lime ; but the proportion of oxide of iron 

 in the ashes it contains never rises above 2.75 per cent. Thus, in 

 100 parts of graphite, there would be at the most 1.9 per cent, 

 of metallic iron ; whereas this substance is commonly regarded 

 as composed of 95 parts of carbon, and 5 of iron. 



