IRON MANUFACTURE. 499 
The fire gradually extends through the mass and expels a portion of 
the volatile material (carbonic acid and water). The method of build- 
ing the piles with coal slack is exactly the same. These piles will con- 
tain from a few hundred to a thousand tons of ore. The length of time 
required to complete the burning will vary from thirty days to six 
weeks, or in the case of some blackbands, some months, according to 
the size of the pile and the kind of fuel, taking more time with coal 
than with charcoal. | 
The evils of this method of roasting are numerous. In the first 
place, the roasting is imperfect, pieces frequently being found among the 
ore almost entirely unburned. 
A prominent charcoal smelter says in regard to the completeness 
of roasting : 
“For the last ten years in this district there is hardly a furnace that has not 
made the serious mistake of burning its ore too lightly. We have done little more 
than smoke it, then have fed it into our short furnaces, and attempted to make the 
best iron. Our ores, and more particularly our gray ores, are especially hard to burn. 
These are found in detached masses in the potters’ clay and fire-clay which overlie 
the regular vein of the ore, large balls from the size of the fist upwards, and it has 
been the universal custom to get them into the wagons somehow, and haul them to 
the kilns, pile them up, putting a little charcoal breeze under them, and smoke 
them.”’ 
Another drawback to this method of pile-roasting is the large 
amount of ore kept on hand, representing money lying idle. In the 
burning of these piles, besides the evil of incomplete roasting, there is 
ever liable to occur, either from the addition of too much fuel or the 
action of winds, local overheating, resulting in the formation of large 
masses of fused or agglomerated material, known by smelters as loups, of 
less value in the furnace than well roasted ore, tending to cause sticking 
or hanging of the furnace and irregular working. The composition of — 
these loups is a silicate of iron, and is similar to that of mill cinder. ) 
Loups are not only produced by high heating, but by .the presence of 
the lower oxides of iron. The higher oxides represented by the hema- 
tites and red ores do not form these fusible masses so readily, and hence 
can be roasted in piles with less danger ; whereas, the carbonates repre- 
sented py the blackbands and blue limestone vores, containing oxide of 
iron as protoxide, form loups very easily, silica making a very fusible 
compound with protoxide of iron, but not with the sesquioxide. 
The cost of this method of roasting is very small, owing to the 
