172 On the Blast Furnace in the Manufacture of Iron. 
1. Changes that take place in the descending mass, composed 
of ore, coal and flux.—By coal is here meant charcoal ; when any 
other species of fuel is alluded to, it will be specified. In the upper 
half of the fire-room, the materials are subjected to a comparatively 
low temperature, and they lose only the moisture, volatile matter, 
hydrogen and carbonic acid that they may contain; this change 
taking place principally in the lower part of the upper half of the 
fire-room. : 
In the lower half of the fire-room, the ore is the only material 
_ that undergoes a change, it being converted wholly or in part into 
iron or magnetic oxide of iron—the coal is not altered, no con- 
sumption of it taking place from the mouth down to the com- 
mencement of the boshes. ' 
From the commencement of the boshes down to the tuyer, the 
reduction of the ore is completed. Very little of the coal is. con- 
sumed between the boshes and in the upper part of the hearth; 
the principal consumption of it taking place in the immediate 
neighborhood of the tuyer. ; 
The fusion of the iron and slag occurs at a short distance above 
the tuyer, and it is in the hearth of the furnace, that the iron com- 
bines with a portion of the coal to form the fusible carburet or pig- 
iron. It is also on the hearth that the flux combines with the sili- 
ceous and other impurities of the ore. This concludes the changes 
which the ore, coal and flux undergo from the mouth of the furnace 
to the tuyer. 
If the fuel used be wood or partly wood, it is during its passage 
through the upper half of the fire-room that its volatile parts are 
lost and it becomes converted into charcoal. M. Ebelman ascer- 
tamed that wood at the depth of ten feet, in a fire-room twenty 
six feet high, preserved its appearance after an exposure for 1} of 
an hour, and that the mineral mixed with it preserved its mois- 
ture at this depth; but three and a half feet lower, an exposure of 
3£ hours reduced the wood to perfect charcoal and the ore to 
magnetic oxide. 'The temperature of the upper half of the fire- 
room when wood is used, is lower than in the case of charcoal, 
from the great amount of heat made-latent by the vapor arising 
from the wood. In the case of bituminous coal, Bunsen and 
Playfair find that it has to descend still lower before it is per- 
fectly coked. 
