230 Dr Colquhoun on the Argillaceous Ore of Iron. 



with any advantage, unless he mixes it in the furnace with ores 

 of a richer quahty. 



The earthy matter is always found to exist in the ore in a 

 state of mere mechanical intermixture. Analogous intermix- 

 tures of foreign ingredients are common in other minerals be- 

 longing to the coal formations ; and the constantly varying pro- 

 portions in which the earthy matter and the ore occur united, 

 can be ascribed only to a mechanical cause of conjunction. 

 Accordingly, if the ore be treated with an acid, the results are 

 quite decisive of the question. If it be taken either in mass, 

 or in the state of powder, and digested for several hours in mo- 

 derately diluted muriatic acid, the carbonate of iron will pass 

 into solution, but nearly the whole of the earthy portion will 

 remain undissolved, the liquid containing mere traces of silica 

 and alumina. The matter which thus remains insoluble, an4 

 which has been detached from the carbonated protoxide of 

 iron, is of a variable composition, being sometimes siliceous, and 

 consisting of minute quartose grains, but more frequently of 

 an argillaceous nature. In the latter case, it is found to consist 

 of both the kind and the general proportions of those ingredi- 

 ents which characterize the ordinary clays, containing silica and 

 alumina, which form the principal constituents, and generally, 

 also, a notable quantity of peroxide of iron, and variable traces 

 of lime and magnesia. From this simple analysis it is evident 

 that the original appellation of argillaceous iron ore which had 

 been suggested by its external appearance, and with which 

 M. Descostils was so much offended, was far from being en- 

 tirely inappropriate. The name of argillaceous carbonate of 

 iron seems to be correctly applicable to the constitution of the 

 ore, and we have therefore adopted it in the present treatise. 



A certain portion of water is also very generally found in 

 the ore, which probably exists in union with the clay, and may 

 be proportioned to its quantity. The amount of this ingre- 

 dient would seem to be seldom less than 1 per cent., for this 

 much was extricated by distillation from an ore which contain- 

 ed an uncommonly small proportion of argillaceous matter, and 

 which, moreover, for some time after having been raised from 

 the pit, had been dried by a free exposure to the atmosphere. 



The carbonaceous or bituminous constituent occurs almost 



