121 
Iron o 
Irtense quantity of materials requisite, as also the conse- 
quent industry exerted to supply one or more furnaces for 
the space of one year. 
When the furnace is sufficiently heated throughout, 
specific quantities of coak, iron-stone, and blast-furnace 
cinders are added : these are called charges. The coaks 
are commonly filled in baskets, which, at all the various 
iron- works, are nearly of a size. The weight of a basket, 
however, depends entirely upon the nature and quality of 
the coal, being from 70 to 1121b, each, '* The iron- 
stone is filled into boxes, which, when moderately heaped, 
contain 561b, of torrefied iron-stone ; they often exceed 
this when the stone has been severely roasted. The first 
charges which a furnace receives, contain but a small pro- 
portion of iron-stone to the weight of coaks : this is after- 
wards increased to a full burden, which is commonly 4 
i baskets coaks, 3201b, ; 2 boxes iron-stone, 1121b. ; 1 box 
blast-fumace cinders, 60 or 701b. f At new works* 
where these cinders cannot be obtained, a similar quan- 
rity of limestone is used. 
The descent of the charge, or burden, is facilitated by 
j opening the furnace below two or three times a day* 
throwing out the cold cinders, and admitting, for an hour 
j at a time, a body of fresh air. This operation is repeated 
I till the approach of the iron-stone and cinder, which is 
* This same variety in the coal renders it almost impossible, 
| iinder one description, to give a just idea of the proportions used 
at various blast-furnaces : to avoid being too diffuse, I shall com 
fine my description connected with a coal of a medium quality, or 
a mixture of splint and free-coal, a basket of which will weigh 
from 78ib. to 84lb. 
- 
t A preference at first is always given to blast-furnace cinders 
in place of lime ; being already vitrified, they are of much easier 
fusion, and tend to preserve the surface of the hearth by glazing 
it over with a black vitrid crust. 
Q 
