50 REPORT- 1839. 



of iron and manganese, over fragments of pit coal. After cooling, the 

 surface of the slag is always found to be altered, and to be covered 

 with a very easily separable layer of graphite, not only where the slag 

 actually touches the coal, but even where it comes in contact with the 

 smoke evolved from the coal. The formation of graphite commences 

 at a temperature lower than 1500° Fahr., and reaches its highest point 

 not much exceeding 2000°. Two different sorts of graphite were 

 produced in this way ; one, which he marked (A), was in elastic 

 scales, of the thickness of writing-paper, with a rather dull metallic ap- 

 pearance. The graphite marked (B) M^as of the thickness of gold-leaf, 

 and extremely light and unctuous to the touch. He found, that all 

 sorts of graphite lost their unctuosity and bright appearance by ex- 

 posing them to the action of concentrated hydro-fluoric acid. Graphite 

 (B) was found to consist of 



Protoxide of iron 18*6000 



Silica 7-6200 



probably mechanically, but equally and invisibly intermixed with 



Carbon 70-3421 



Silicon 3-0744 



Loss 00-3635 



Graphite (A) gave. 



100-0000 



4-93 Silicon. 



9-50 Iron. 

 85-45 Carbon. 

 00-12 Loss. 



100-00 



The quantity of oxides of iron and silica had been ascertained by 

 heating the specimens first with acids and caustic leys ; the quantity of 

 carbon, by burning the specimens with chromate of lead and chlorate 

 of potash ; and the silicon, by melting the powders with carbonate of 

 soda in a platinum crucible. He considered, therefore, the graphite 

 to be a carburet of silicon and iron ; and showed, by heating in a pecu- 

 liar way the remainders, left after the solution of iron in hydrochloric 

 acid of a certain specific gravity, that the chemical composition of cast 

 iron, in its two distinct species of gray and white cast iron, had direct 

 relation to the two specimens of graphite, and in all probability was 

 derived from similar origin, as indicated in the following table : 



Graphite (B). Gray Cast Iron. 



Smcon I Oxygen. Silicate of iron. 

 Carbon j Carburet of silicon. 



e-,- I Silicet and alummet 



Silicon > p . 



/ A 1 • \ I of iron. 

 (Aluminum) J 



SmcoT} Carburet of iron. 



