Dr Colquhoun on the Argillaceous Ore of Iron. 77 



one or other, or with several of these substances, it assumes a 

 different character in the eyes of the ironsmelter, and must be 

 differently treated by him in respect of the preparatory calci- 

 nation and the appKcation of his fluxes. There are still other 

 occasional constituents of the ore which are fortunately of 

 comparatively rare occurrence, but which bear so very decided a 

 character in their effect on the operations of the iron manufac- 

 turer, that it is indispensable to take some notice of them here. 

 These are sulphur and phosphorus. Keeping in view these 

 ingredients, as each of them constituting a distinct class of 

 ironstones, according to its predominance, we shall find that 

 the ore must be divided into the following classes. Besides 

 first, the pure carbonate of iron, the preponderance of bitu- 

 men or coal will form the second class or hituminoits carbonate 

 of iron. When sand is the principal ingredient, as this re- 

 quires to be treated with a pecuUar kind of flux, it will form 

 a third class, the siliceous carbonate of iro7i. If clay be a 

 large constituent of the ironstone, for the same reason, it forms 

 a fourth class, the argillaceous carbonate of iron. This is 

 by far the most abundant variety of the ore; and when the 

 amount of clay Hes within moderate limits, it affords a cast- 

 iron of excellent quality. As the same set of fluxes act, with 

 nearly equal effect upon lime and upon magnesia, and be- 

 sides, as the carbonate of magnesia, when it occurs in the 

 ore, is almost invariably accompanied by carbonate of lime, 

 these two constituents, which are both alkaline earths, may 

 be said to possess but one character, and to form, in re- 

 gard to the metallurgist, but one class of ores, the fifth in the 

 present order, and which may be called the calcareous carbo- 

 nate of iron. When it happens that several of these extra- 

 neous substances enter into the composition of the mineral, a 

 different mode of treatment by the smelter is required, and 

 new classes of the ore are thereby formed. These seem to be 

 fitly described, according to the respective preponderance of 

 the mixed ingredients, and form, sixth, the calcareo-siliceous, 

 if sand be the principal and lime the secondary constituent ; 

 seventh, the calcareo-argillaceous, if clay hold the place of the 

 sand in the previous blass ; eighth, the bitumino-siliceous, if 

 coal or bitumen be the ingredient that is associated in the ore 



