4)2i Dr. Schaf haeutl on the Different Species of 



the silicates of the slag by depositing a great quantity of finely 

 divided coal, as is sometimes the case in gas retorts. 



If we assume the puddling slag to consist of a mixture of dif- 

 ferent silicates, from which thesesquisilicate of iron very often 

 separates itself during the process of cooling, we may easily con- 

 sider that one atom of the silica of the sesquisilicate is reduced 

 to silicon, combining with the superabundant carbonaceous 

 matter, in the nascent state, into a carburet of silicon, which 

 Avith the other three atoms of protoxide of iron and one atom 

 of silica, remains mechanically mixed; and, indeed, when we 

 consider the before-mentioned parts of graphite (b) extractable 



by acids and alkalies, we come very near the formula F^ S 

 [Silicias triferrosiis). 



On the contrary, with graphite (a), both constituents of the 

 slag, oxide of iron and silica, appear to be reduced, and 

 combining with carbon into supercarburets; and these two dif- 

 ferent chemical compounds are easily explained by the differ- 

 ent degrees of heat by which they are generated, and the 

 length of time allowed for their formation. 



These two singular and differing species of graphite ap- 

 pear to be the prototypes of the two different species of cast 

 iron, as is shown in the following tables. 



Graphite {b.). 

 sVc ' " ' ' ^ Oxygen, Silicate of iron. 



Silicon 



> Kj&xnmn 



Graphite {a). 



Carbon.", r^'"^'"'"^*''^'''^'^" 



Iron . . , 

 Carbon , 



Carbon , 

 Silicon . 



Carburet of iron. 

 Carburet of silicon. 



Gray Cast Iron. 



J,™."^ 1 Silicet and alu- 



^^l^^^"." f minetofiron. 



Aluminum . J 



Carbon "1 Carburet of sili- 



Silicon J con. 



Wliite Cast Iron. 



Iron "I Carburet of iron. 



Carbon .... I Cyanuret of 



Azote J ( iron ?) 



Silicon 1 Carburet of Sili- 



Carbon ...j con. 



The molecules of all sorts of iron, the elementary parts 

 of which are perceptible by the aid of a magnifying glass, be- 

 long to the cubical system, generally of equal size, of which 

 the largest grain never exceeds 0*0000633 of an inch; their 

 form appears to be always the same, and their different modes 

 of aggregation in the various sorts of iron is all that can me- 

 chanically form the difference between cast and malleable iron, 

 as far as ocular inspection, assisted by magnifying glasses, can 

 penetrate. 



Iron in which those molecules are aggregated in the most 

 perfect crystalline form, having all their faces in one plane of 

 crystallisation, is called perfect dark-grey iron. 



Some tendency of the molecules to crystallize by their ar- 



