277 
Steel. 
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 effectu- 
ally prevent the cementation. When the fire is put into 
the grate, the heat passes round by means of flues, made 
at intervals, by the sides of the trough. The fire is con- 
tinued 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. 
If they be not sufficiently changed, the hole is again 
closed carefully, to exclude the air ; but if, on the contra- 
ry, the change be complete, the fire is extinguished, and 
the steel is left to cool for a few days more, when the pro- 
cess for making blistered steel is finished. For small 
wares, the bars are drawn, under the tilt hammer, to about 
half an inch broad and three- sixteenths of an inch thick. 
The change wrought on blistered steel by the tilt hammer, 
is nearly similar to that effected on iron from the refinery 
by the forge hammer. It is made of a more firm texture, 
and drawn into convenient forms for use. German steel 
is made by breaking the bars of blistered steel into small 
pieces, and then putting a number of them into a furnace ; 
after which they are welded together and drawn to about 
eighteen inches long; then doubled and welded again, 
and finally drawn to the size and shape required for use. 
This is also called shear steel, and is superior in quality 
to the common tilted steel. Cast steel is also made fron> 
the common blistered steel. The bars are broken, and 
* Or with 4 inches deep of moist sand. Indeed the clay should 
be covered with a layer of sand, to fill up the cracks made by the 
heat. 1001b. of iron gains half a pound by being converted into 
blistered steel- T. C> 
