Reduction of Iron and Silver Ores. 215 



It requires much care, and practical knowledge, so to arrange the 

 fusibility of the flux, as to obtain the greatest quantity and best qual- 

 ity of iron. 



Whatever earths may be mixed, or combined in the ores, they may 

 always be rendered fusible by adding two others. It is necessary, 

 however, to observe, that lime, alumina, and magnesia will not fuse 

 together, but any two of these, with silex, or metallic oxides, will form 

 a glass. Magnesia tends to diminish the fusibility of the substances 

 with which it is mixed. 



The usual fluxes are marl, limestone, and clay. Limestone is 

 often used when it ought not to be, and the same may be said of 

 marl. In Sweden, mica and mica slate, hornblende, garnet, basalt, 

 actynolite, argillite, he. are used as fluxes, and, in many parts of this 

 country, these materials might be employed, with advantage. 



Manganese fluxes most readily with silex, and this is what should 

 be used in ores containing that metal, unless they already contain an 

 excess of silex, and then, limestone should be used. 



The fluxes to be used will be determined, 



1. By the nature of the earths already combined, or mixed in the 

 ore or ores ; 



2. By their quantity ; 



3. By the nature of the mineral substances in the vicinity. 



It is often advantageous to mix different ores, so that the impuri- 

 ties may flux with each other. 



The cinder (laitier) formed by the fusion of the flux and the im- 

 purities of the ore, to be of the best quality, should not begin to melt 

 until the iron is deoxidized, or nearly so, and sufficiently carburetted. 

 It should have such a degree of viscidity as to remain adhering to, 

 and enveloping the mineral in which the earthy matter is mixed, or 

 combined, so as to prevent the oxidation of the iron, as it melts and 

 falls into the crucible of the furnace ; but the viscidity should not be 

 so great as to prevent the globules of iron from sinking through the 

 semi-fluid cinder which floats over the melted iron in the crucible. 



The cinder, when the iron is of good quality, is often of a light 

 gray, or of a whitish color. The French call the cinder laitier, from 

 its color. 



3. Cast Iron. 



Of these, there are three principal varieties, viz. gray, mottled, 

 and white. They are too well known to need description. Hassen- 



