46 
[AsSEMBLr 
ores just referred to. It sometimes, however, contains, as we are 
informed by Dr. Thomson, a portion of carbonate of lime, and is 
also associated with quartz and with hornblende. In the process 
of reduction the ore is broken into small pieces, roasted, and then 
put into conical shaped furnaces, constructed of the slag from cast 
iron, which is found to answer the purpose fully as well as bricks, 
and to ccme much cheaper. In these furnaces it is mixed with the 
requisite quantity of charcoal, but the addition of limestone is sel- 
dom necessary, because it exists already in the ore. Here it is 
melted and separated from the slag, which is allowed to run off, or 
is cast into bricks, according as it is wanted. The cast iron ob- 
tained by this process, is as white as silver, very hard and brittle, 
and is not liable to rust; but in this state it can not be applied to 
any useful purpose in consequence of its brittleness. This iron is 
converted into malleable iron by heating it in a bed of charcoal 
and oxide of iron, and hammering it out into bars while hot. In 
this state it is whiter than common iron, of a distinctly fibrous tex- 
ture, and is much stouter than any species of iron whatever.* 
There is still some uncertainty in regard to the cause of the su- 
periority of the Dannemora iron. By some it is ascribed to the 
presence of manganese. Berzelius supposes it due to the presence 
of the metallic basis of silica. Another author again refers the su- 
periority to the mixture of carbonate of lime which the ore contains. 
And finally, it has been ascribed principally to the process employ- 
ed, for it is asserted that by following a similar mode of manufac- 
ture, as good iron has been obtained from other Swedish ores as 
from that of the Dannemora mine. 
In those parts of the State where what are called high furnaces, 
are in use, the leading principles of the process of smelting are 
well understood, and in some cases a considerable degree of per- 
fection has been attained. But so many circumstances enter into 
the iron smelter's manufacture, and an attention to each of them is 
so important to the success of the whole, that with so few of the 
necessary data which we possess, it is a striking proof of the ingenui- 
ty of our countrymen, that they have been enabled to prosecute it 
with even tolerable success. It is now admitted, that in order to 
carry on this branch of art in the most advantageous manner, it is 
essential that the chemical composition of the ore should be accu- 
* Dr. Thomson's Travels in Sweden. 
