D. CHEMISTRY AND METALLURGY. 65 



GRAPHITE IN GRAY OXIDE OF IRON. 



From recent investigations of Sneller, we are informed that 

 the graphite segregated in gray oxide of iron consists of pure 

 carbon, but that there is no free graphite-like silicon associ- 

 ated with it, although some occurs in combination. The 

 quantity of carbon which remains enveloped in the harden- 

 ing of a fluid cast-iron appears to be dependent on the pro- 

 portion in which the carbon was dissolved in the liquid iron, 

 and upon the rapidity with which the transformation took 

 place from the liquid to the solid state, rather than upon the 

 quantity of foreign elements, such as manganese, sulphur, 

 phosphorus, silicon, etc., thus not upon the height of the tem- 

 perature at which the iron was treated. While in puddling, 

 nearly all the silicon is burned before the carbon becomes 

 oxidized, this process of oxidation in the Bessemer method 

 comes on about equally with the two elements, if not even 

 more rapidly with the silicon. The remarkable fact that the 

 same amount of silica which makes the Bessemer and cast 

 steel cold-short does not affect the quality of wrought iron 

 under all conditions appears to depend upon the circumstance 

 that steel contains the silica in a state of chemical combina- 

 tion, while in wrought iron it only occurs as a slag. 1 8 (7, 

 xi., August 2, 493. 



FORMATION OF PLUMBAGO. 



The presence of plumbago in gneiss, mica slate, clay slate, 

 granular limestone, etc., according to Dr. R.Wagner, is de- 

 pendent upon the chemical reaction of the decomposition of 

 cyanogen and its combinations. This is illustrated, and in a 

 measure proved, in Dr. Wagner's opinion, by the formation 

 *of graphite, as has been seen to take place in Le Blanc's soda 

 manufactory. At a certain sta^e of the transformation of the 

 soda into caustic soda cyanogen undergoes a decomposition, 

 and graphite, or plumbago, is developed in abundance upon 

 the surface of the lye. The amount produced is so great as 

 to have suggested a source for graphite in the manufacture 

 of lead-pencils, should the mines of the natural material ever* 

 fail. Quite large masses of this graphite are obtained as a 

 secondary product of the soda-works in a chemical establish- 

 ment at Aussig, in Bohemia. 14 C, CXCVIIL, 176. 



