of the Argillaceous Iron-Ore. 269 



ways more or less deeply coloured, in consequence of the ox- 

 ide of iron which the excess of silica holds in a state of combi- 

 nation. 



If the scoria present the appearance of being completely 

 melted, and has a vitreous and somewhat enamelly aspect ; 

 and if it is at the same time unusually free from colour, this 

 is a proof that the lime has been adjusted in its due propor- 

 tion to the other earthy ingredients of the assay. The colour 

 by which such scoriag are generally distinguished is a light 

 shade of grey. 



If the scoria be marked by a green colour, this indicates the 

 presence of manganese. It is necessary to observe, however, 

 that it would be unsafe to estimate the quantity of manganese 

 solely from the degree of intensity of the green colour; for 

 when the ignition in the assay furnace is violent and protrac- 

 ted, the oxide which the slag had originally held in solution 

 undergoes reduction, and, coalescing with the iron, forms part 

 of the metallic button. 



But if, instead of obtaining the scoria fully and distinctly 

 separated from the metallic product, the whole assay, on open- 

 ing the crucible, be found to exhibit a scoriaceous mass, usual- 

 ly of a greyish or blackish colour, attractible strongly by the 

 magnet, and containing particles of iron diffused throughout 

 its entire substance, this result indicates, that although the ox- 

 ide has been reduced in the furnace, yet some of the earths 

 have been present to excess during the assay, and that the flux, 

 either from its amount or its composition, has wanted the re- 

 quisite degree of energy to liquefy the mass, and to unite the 

 metallic particles into a button. Sometimes this product will 

 present the appearance of having undergone a mere incipient 

 fusion, and will be in the state of an incoherent and easily 

 friable mass ; or it may even have undergone a viscous semi- 

 fusion, so as to be left in the shape of a solid opaque mass, 

 very difficultly frangible, and breaking with a compact stony 

 fracture. 



Unfortunately, a scrutiny of the external characters of the 

 metallic button cannot lead to any conclusions regarding the 

 value of the metal to be obtained by smelting the ore, with 

 the same degree of precision with which a similar investiga- 



VOL. VIII. NO. II. APRIL 1828. s 



