PONTO an 
Observations on Iron and Steel. 417 
have had a pretty good appearance; but the edges 
are not firm, and they soon lose their polish. Com- 
mon table knives are frequently made of this metal. 
The cementation of iron converts it into steel :-— 
a substance intermediate between crude and malle- 
able iron. . 
The furnaces for making steel are conical build- 
ings; about the middle of which are two troughs of 
brick or fire-stone, which will hold about four tons of 
iron in the bar. At the bottom is a long grate for fire. 
The steel furnace, however, is not well adapted for 
description. I shall therefore avail myself of an 
accurate drawing, which was communicated to me 
by a gentleman conversant with the manufacture, 
and which is copied in plate I, page 122. 
A layer of charcoal-dust is put upon the bottom 
of the trough; and, upon that, a layer of bar iron, and 
so on alternately until the trough is full. It is then 
covered over with clay to keep out the air; which, if 
admitted, would effectually prevent the cementation. 
When the fire is put into the grate, the heat pas- 
ses round by means of flues, made at intervals, by 
the sides of the trough. The fire is continued until 
the conversion is complete, which generally happens 
in about eight or ten days. There is a hole in the 
side by which the workmen draw out a bar occasion- | 
ally, to see how far the transmutation has proceeded. 
This they determine by the blisters upon the surface 
of the bars. Ifthey be not sufficiently changed, the 
hole is again closed carefully to exclude the air ; but 
