228 Dr Colquhoun on the J?'gillaccons Ore of Iron. 



ore, as well as an account of the history of the art and an ex- 

 position of its principles. It is true that Mr Mushet's theories, 

 when he indulges in them, are often more ingenious than solid ; 

 but in regard to everything which a penetrating observation, 

 and ready apprehension, aided by a most extensive experience, 

 can furnish to a practical man, his works are unrivalled in this 

 country and on the continent. 



We shall now proceed to examine the nature and constitu- 

 tion of the ore of iron. This is a subject which presents it- 

 self under various interesting views, and it is material that 

 none of these be overlooked. Thus, the design of this trea- 

 tise requires that we should fix the precise mineralogical 

 rank of the ore of iron ; yet, as our leading object is to con- 

 vey m^tallurgic instruction, it is not enough to detail the ex- 

 ternal and physical characters of the mineral, or to divide it 

 into all its different varieties, so as to assign it an accurate 

 place in the cabinet of the natural philosopher. It is not 

 enough to explain in what geological situations it occurs, al- 

 though this also is an interesting part of its history. For it is 

 far more material to the smelter of iron to be informed of the 

 chemical composition and affinities of the various constituents 

 which form the ore, and distinguish its varieties, in order that 

 he may be aware under what treatment he is most likely to be 

 successful in compelling it to yield up the metal which it con- 

 tains. 



In considering the nature of the ore of iron under these dif- 

 ferent views, we shall adopt the following order. — In the first 

 place, we shall examine the ore by its external and physical 

 characters, so as to be able to submit a mineralogical arrange- 

 ment of all the various forms under which it is found. In the 

 n^xt place, we shall consider its geological character. And, in 

 the last place, we shall distinguish the ore into the classes 

 which are suggested by a regard to its chemical composition 

 and affinities, the properties which exclusively engross the at- 

 tention of the iron smelter. 



The argillaceous carbonate of iron consists essentially of the 

 protoxide of iron united to carbonic acid, and it bears the 

 same relation to the crystallized carbonate of iron or sparry 

 iron ore, which common compact limestone has to calcareous 



