MANUFACTURE OF IRON. 41 



in its characters to the primitive or magnetic ores found m the northern and southern parts of 

 the State. It sometimes, however, contains, as v^^e 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 come much cheaper. In these furnaces, it is mixed with the requisite 

 quantity of charcoal ; but the addition of limestone is seldom 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 obtained by this process 

 is as white as silver, very hard and brittle, and is not liable to rust ; but in this state it cannot 

 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 cominon iron, of a distinctly fibrous tex- 

 ture, and is much stouter than any other species of iron whatever.* 



There is still some uncertainty in regard to the cause of the superiority 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 superiority to the 

 mixture of carbonate of lime which the ore contains ; and finally, it has been ascribed prin- 

 cipally to the process employed ; for it is asserted, that by following a similar mode of manu- 

 facture, as good iron has been obtained from other Swedish ores as from that of the Danne- 

 mora mine. 



In those parts of the State where what are called high furnaces arc in use, the leading 

 principles of the process of smelting are well understood, and in some cases a considerable 

 degree of perfection 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 it may be regarded as a striking proof of tiie ingenuity of our countrymen, that 

 with so few of the necessary data, 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 advanta- 

 geous manner, it is essential that the chemical composition of the ore should be accurately 

 determined, as well as that of the flux to be used, of the slag or scoria formed during the 

 process, and finally of the iron which is the result. Investigations of this kind have been 

 prosecuted for some years in Sweden, France, Germany and England ; and the result has 

 been the introduction of improvements, by means of which the ores iiave been made to yield 

 a larger quantity and a better quality of iron than was formerly obtained from them. 



It has already been stated, that when the ore is of great purity, the process of reduction is 

 exceedingly simple. But as the ores most generally used contain earthy bodies, as sihca, 

 alumina, &c. in considerable proportions, the business of the iron smelter consists in fusing 

 the earths, and in deoxidizing the ore by the agency of carbonaceous matter. But silica, when 



* Dr. Thomson. Travels in Siveden. 

 P.\RT I. 6 



