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 sort of supercarburet of silicon, which is called 
graphite^ or by the iron-smelters, Msh, 
I procured a beautiful specimen of this sort of graphite or 
hish 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 
increasing 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 Pliil. Mag. 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 AM , — Edit.] 
