Dr Colquhoun on the Jssat/ 



that these earths are associated with one another in iron ores, 

 so adjusted in their nature and relative proportions as to form 

 easily fusible compounds, it is necessary for the smelter to con- 

 sider what are the earthy ingredients in any given ore, so 

 that he may adapt thereto such a flux as will cause the whole 

 mixed mass readily to melt in the furnace upon a due appli- 

 cation of heat. 



Thus it appears that it is of primary importance to attend 

 both to the nature and to the proportions of the various earths 

 which are brought together in the furnace. Now, as there is 

 a considerable variety in the kinds of those earths with which 

 iron is associated by nature, and as there is an endless chang- 

 ing in their relative proportions, it is essential that the smelter 

 should possess some knowledge of the composition of any 

 given ore which is to be assayed, in order that he may be 

 enabled to prepare the most appropriate flux for it, — that flux 

 which shall fuse it most perfectly, and produce as the result 

 of the assay, the true amount of metal which the ore contains. 



In selecting and adjusting his flux, the assayer ought always 

 to have in view the following circumstances. First, the use of 

 a substance which, while it is unexceptionable in other respects, 

 is of such a nature as is best adapted to liquefy the ore at the 

 lowest temperature. Second, the exhibition of this flux in suf- 

 ficient quantity to fuse the whole of the ore ; and third, the 

 limiting of its amount within such bounds, that the whole of 

 it may be engrossed in absorbing and liquefying the whole of 

 the earthy ingredients of the ore. For if an excess of flux be 

 employed, it has often the strongest tendency to form a new 

 ore within the crucible, owing to the disposition of oxide of 

 iron to unite, at a high temperature, with an earthy mixture 

 and to vitrify it. So much indeed is this the case, that the 

 most accurately adjusted fluxes always retain a certain portion ^ 

 of the metal unreduced ; and the amount of this very rapidly 

 augments when an excess of earthy matter is exhibited. 



Nothing therefore can be more important to the successful 

 operation of smelting, whether on the greatest or the smallest 

 scale, than an accurate knowledge of the nature and relative 

 proportions of the earthy constituents of an ore. This is the 

 only sure means that the ironsmelter can possess for directing 



