Cast Iron, Steel, and Malleable Iron. 419 



these substances in the process from the clay of the melting* 

 pots. 



These pure, charcoals, which I analysed, I found, both be- 

 fore and after their exposure to the highest degree of tem- 

 perature, invariably to consist as follows : 



1st, Of carbon, hydrogen, and traces of potassium not ex- 

 tractable by acids. 



2ndly, Carbon, hydrogen, nitrogen; and these charcoals 

 never parted from their hydrogen, &c., unless they had the 

 opportunity of combining with silicon or aluminum or iron 

 instead. 



Graphite or plumbago is sometimes an artificial product, 

 and separated from the iron on the hearth of the blast furnace 

 in the process of making gray Jcishy cast iron, that is to say, 

 by using a very easily fusible mixture of limestone and iron 

 ore, and keeping up a great heat in the furnace. This arti- 

 ficial plumbago is called by the workmen kish *. Good white 

 charcoal iron, which is for sometime kept in a high degree of 

 temperature, and afterwards very slowly cooled, is invariably 

 converted into gray iron ; so, in like manner, gray charcoal 

 iron may be converted by sudden cooling into white. 



As the generation of kish and gray iron never takes place, 

 except during the hot working of the blast furnace, the con- 

 clusion was drawn by Karsten that graphite or kish could 

 only be generated in the highest degrees of temperature ; and 

 he was led by this circumstance to infer, that by treating iron 

 ores in small crucibles with charcoal, white iron was always 

 obtained, and very seldom gray iron. 



I shall, however, show that the generation of graphite com- 

 mences at 1500 degrees Fahr., measured with Daniell's pyro- 

 meter, a degree in which even brass remains in its rigid 

 state. 



In some works where gray cast iron or pig iron is imme- 

 diately converted into malleable iron, without undergoing first 

 the process of refining, the hearth of the puddling furnace re- 

 mains half filled with a kind of liquid slag, which consists 

 principally of a trisilicate of iron and manganese. In this 

 liquid mass the raw pig iron is converted, during a rapid 

 effervescence of the whole, into malleable iron, and the 

 slags, after the operation, run off into small cast iron boxes, 

 over the bottoms of which is spread coal-dust, to prevent the 

 slag from adhering to the bottom and sides of the boxes. As 

 soon as this slag runs over this coal-dust, a vivid evolution of 



[On this subject see a paper by Mr. (now Professor) E. Davy, Phil, 

 Mag. First Series, vol. xl. p. 41, 44. — Edit.] 



2E2 



