Cast Iro7ii Steel, and Malleable Iron. 421 



where the graphite pellicle originated, was likewise altered; 

 the surface of the common puddling or balling slag is of a dull 

 blueish or of a somewhat slaty appearance, originating in the 

 closely interwoven angles of the crystals, which constitute the 

 mass of the slag. But in this case the 'whole space of the slag 

 covered with the pellicle of graphite, presented a glassy 

 shinmg appearance, resembling dark green bottle glass ; and 

 viewed through a microscope had a velvety appearance, that 

 is to say, was formed of small points with circular intervals, 

 which caused an interference of the rays of light, and was 

 therefore coloured with the usual bands originating under 

 such circumstances. 



The manner in which this graphite pellicle was formed, 

 shows distinctly that not only carbonaceons matters are re- 

 quired for generating graphite, but that a silicate of iro?i ajid 

 manganese is indispensably necessary ; for the reason, that no 

 other substance is capable of forming graphite with coaly 

 matter; and secondly, principally because the pellicle was 

 not only mechanically an interlay er of crystallized carbon be- 

 tween the two slags, but it actually rose out of the surface of 

 the slag, had taken up a portion of the surface, and finally lost 

 and immerged itself entirely in the surface : but at the same 

 time highly bituminous coal is necessary. 



The coal of Rive de Gier, near Lyons, in France, produces 

 readily and plentifully pellicles of graphite; the coals of 

 Alais, Pont du Gard, on the foot of the Cevennes, which 

 contain very little bitumen, produced only an inseparable 

 powdery or scaly layer of plumbago or graphite. 



The graphite produced by the before-mentioned means must 

 be divided into two different species. 



Graphite (a), generated about the thickness o{ paper, always 

 consists of elastic leaves of a rather dull blueish appearance, 

 similar to that of annealed sheets of iron. 



Graphite {b), about the thickness of gold-leaf, is shiny, 

 extremely light, and to the touch similar to natural plum- 

 bago. 



AH species of plumbago are considered unalterable in all 

 kinds of acids ; but I found that concentrated hydrofluoric 

 acid changes their nature entirely, and converts all descrip- 

 tions of plumbago which have hitherto come under my ob- 

 servation, into a flocky light dull carbonaceous mass, during 

 the escape of fluo-silicic acid gas. 



Plumbago has of late been burnt in the muffle of an assay 

 furnace, in order to separate the foreign non-volatile bodies. 

 This mode of procedure is ineffective, as the current of air 

 and the rising carbonic gas carry away with them the great- 



