Iron • 
201 
purposes to arrange the several kinds of cast iron under 
one or other of the four following subspecies* 
1. Smooth faced Iron , or No, L of the manufacturers. 
This seems to be composed of iron supersaturated with 
carbon, and mixed with a comparatively small proportion 
of oxyd and earthy impurities. Its upper surface is 
smooth and convex, entirely free from oxyd, and often 
covered with a thin crust of plumbago : it presents a 
coarse granular fracture with a brilliant metallic lustre 
and a dark blue colour. 
2. Good melting pig Iron , or No. 2. of the manufac- 
turers. This differs from the preceding in containing pro- 
bably a smaller portion of carbon and a larger admixture 
of oxyd of iron. Its upper surface is slightly convex and 
full of small cavities : its fracture is coarse granular to- 
wards the centre of the pig, but the concretions manifestly 
diminish in size as they are situated nearer the surface ; 
its colour is dark grey inclining to blue. 
3. Grey Iron , or No. 3. of the manufacturers. In this 
the amount of carbon is still further diminished. Its upper 
surface is level, sometimes slightly concave, and presents 
more and larger cavities than the preceding, it is slightly 
oxydated superficially ; its fracture is fine granular, and 
its colour is light grey. 
4. White Iron , forge pigs , ballast Iron . In this the 
quantity of combined carbon is smaller and the admixed 
oxyd larger than in any of the preceding. Its upper sur- 
face is concave, rough, and covered with a plate of oxyd ; 
its fracture is compact sometimes tending to striated, its 
colour is tin- white, occasionally mottled with grey. 
We shall now proceed to state in a general way, the 
circumstances in the smelting which principally influence 
the quality of the produce. Much depends on the fuel ; 
if the cokes are not perfectly made but retain a part of 
their bitumen, the whole mass cakes together in the upper 
C c 
