of the Argillaceous Iron-Ore. 259 



casioned by the muriatic acid attacking and dissolving the carbo- 

 nate of iron, and any other carbonate, as of lime, magnesia or 

 oxide of manganese, which may exist in the ore. When the 

 whole muriatic acid has been added, expose the mixture to a mo- 

 derately warm temperature, that of a sand-bath, for example, and 

 agitate it frequently, so as to expose every particle of the ore to 

 the direct action of the acid, and to prevent the undissolved por- 

 tion from concreting into a mass. At the termination of about 

 an hour, the whole of the oxide of iron, lime, magnesia, and 

 oxide of manganese, will have been taken up by the acid ; and 

 the portion left undissolved will consist of clay, together with 

 silica, if the ore has been of a siliceous nature, and of carbo- 

 naceous or coally matter. Let the whole be now transferred 

 upon a small paper filter, and the insoluble residue washed, 

 so long as the liquid which passes through has a perceptible 

 taste of acidity. Then dry the filter, first between folds of 

 blotting paper, and afterwards before a fire or upon a sand- 

 bath : it should now be put together with its contents, into a 

 platinum crucible, and calcined, either over the flame of a large 

 spirit lamp or upon pieces of red hot wood charcoal, until the 

 carbonaceous matter produced by the ignition of the paper 

 and the coally matter originally contained by the ore, is en- 

 tirely .consumed. The residue will consist of the clay and si- 

 lica of the ore in a state of separation from all the other in- 

 gredients ; and its weight will of course indicate the propor- 

 tion which the ore contains of argillaceous or siliceous matter. 



After having thus ascertained the proportion of clay which 

 is present in any ore that is to be assayed, the amount of lime 

 which is to be employed as a flux will be carefully adjusted to it. 

 In most cases a quantity amounting to three-eighths of the 

 clay will be found the most efficacious adaptation. But if ac- 

 tual experiment should prove that a larger supply of lime is 

 requisite, it may be inferred that the clay is unusually abun- 

 dant in silica ; and if, on the contrary, a smaller quantity of 

 lime suffices, it is probable that the ore naturally contains a 

 certain portion of the carbonate of lime. 



We have now briefly considered the ores in which clay or 

 silica is a preponderating ingredient. Those which are usual- 

 ly styled calcareous seldom contain a sufficient quantity of 



