of the Argillaceous Iron-Ore. 251 



We shall consider the two processes separately : and shall 

 commence with the dry assay. 



§ 1. On the Dry Assay of Ironstones. 



In performing this assay, the leading object to be kept in 

 view is to effect it accurately, in the most rapid manner, and 

 on the smallest scale. It ought to be in all respects a minia- 

 ture model of the process which is afterwards to be employed 

 in smelting the ore in the blast furnace, and it is only when 

 this point is pretty nearly attained that much reliance can be 

 placed upon the conclusions deduced from the assay. In ex- 

 plaining therefore what is essential to the successful manage- 

 ment of the dry assay, it seems of importance to keep in view, 

 at the outset, the history of the smelting process. After a 

 brief glance at this, the details which more exclusively belong 

 to the assay will be better appreciated. 



Metallic iron nowhere exists in a native state to any con- 

 siderable extent, ^hat metal must always be extracted from 

 its combinations with oxygen and the admixture of certain 

 earthy bodies, by fusing the earths, and by deoxidating the 

 metal through the agency of carbonaceous matter. When the 

 earthy constituents of the ore are brought into this state, the 

 particles of metal which they include will subside through 

 the fluid by their superior specific gravity, and unite at the 

 bottom of the furnace in which the smelting takes place ; so 

 that when the whole is allowed to cool, the metal will be found 

 collected in a solid lump at the bottom, while the earthy in- 

 gredients are lying above in the shape of a vitrified and homo- 

 geneous mass. In all cases of assay, the metal which is thus 

 found below is called the metallic button, and the superincum- 

 bent vitrified earth is named the scoria. 



There is no single earth of those which are usually found 

 in ironstones, that can be brought into a state of fusion by 

 the application of any heat of a furnace, however intense. But 

 in some binary compounds of these bodies, and in many ter- 

 nary compounds, the ingredients are found to act mutually 

 on each other so as to yield to the heat of a furnace, and will 

 soften into a porcelain, or melt into an enamel, or flow into a 

 liquid glass, as the case may be. But as it rarely happens 



