588 Dr. Schafhaeutl on the Different Species of 



The crystalline form of cast iron generally depends on the 

 relative atomic combination of carbon with silicon. The 

 hardness and whiteness of the compound decreases with the 

 increase of carbon, and has reached its utmost degree of 

 friability in that sortof supercarburet of silicon, which is called 

 graphite, or by the iron-smelters, kish. 



I procured a beautiful specimen of this sort of graphite or 

 kish a few weeks ago from one of the blast-furnaces at Mer- 

 thyr-Tydvil. A rather porous piece of slag, of a yellowish 

 green colour, like impure sulphur, was found to be interwoven 

 with a graphitic formation, consisting of large irregular layers 

 of different sizes, and of a dusty grayish graphitic hue. These 

 large layers or laminae were found to be composed of smaller 

 rhombic scales, lying one over another, similar to the tiles 

 of a roof, and giving to the surface the appearance of a regu- 

 lar rhombic network *. 



The composition of the large laminae was found to be 

 different in different parts of their thickness. The scales of 

 graphite on the outside were soft, light, and so easily divisible 

 as to soil the fingers. They increase in thickness and 

 become more dark-coloured towards the middle, and the 

 central layer had the appearance and hardness of black cast 

 iron, and its somewhat conchoidal fracture had a lustre be- 

 twixt those of glass and pitch. The exterior and thinnest 

 scales were not attracted by the magnet at all; but the interior 

 ones were affected by the magnet almost in the ratio of their 

 increasino; thickness. 



In hydrochloric acid, the central layer evolved hydrogen 

 rapidly, first a white, and afterwards a yellowish scum of si- 

 lica were separated, and it showed in fact all the properties 

 of the blackest cast iron. 



The scales adjoining were strongly attracted by the magnet, 

 and appeared under the microscope to be covered with small 

 flattened crystals, forming an irregular six-sided prism, of 

 which only four sides were developed; in a similar manner 

 only two opposite sides of the rhombic faces of each end of 

 the crystal were left, corresponding to the smaller sides of 

 the prism. 



Those small crystals seemed to constitute a central point, 

 from the sides of which the small leaves of graphite forming 

 the surface of the laminae appeared to radiate. 



I succeeded in separating one of those largest crystals, and 

 in covering it under the microscope with a drop of concentrated 



* [In Phil. I\lag. First Series, vol. xl.p. 41, will be found an examina- 

 tion, by Mr. (now Prof.) E. Davy, of a native graphite considered by him 

 strongly to resemble Aw/^— Edit,] 



