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284 Dr Colqulioun on Argillaceous Iro7i-Ore. 



eight grains of this into a small shallow platinum capsule, and 

 ignite them over the flame of a spirit lamp. As long as any 

 smoke continues to be evolved, the heat must be applied with 

 extreme caution, and the powder must be incessantly stirred. 

 When all the bituminous portion of the coal has been volati- 

 lized, the temperature ought to be raised as high as possible ; 

 and in order to maintain it at this pitch, the lid of a platinum 

 crucible may be placed over the capsule, so as to reflect the 

 heat back upon the powder. At the end of about ten minutes, 

 the whole of the carbonaceous matter will be consumed : an 

 addition of six or eight new grains of the powdered coal is now 

 therefore to be put into the capsule, and after having been 

 mixed up with the earthy matter already formed, it is to be 

 burnt with the same precautions as in the first calcination. Let 

 this process be repeated several times in succession, until it ap- 

 pears that a sufficient quantity of the earthy residue has been 

 obtained ; after which, the weight of this residue deducted from 

 the total weight of the original coal, will give the relative pro- 

 portions of combustible and incombustible matter in the coal. 



We have directed that the heat should always be applied 

 very gradually at the commencement of the ignition. If the 

 opposite course be followed, the smoke which is given ofi^ will 

 speedily catch fire, and the pounded coal will be converted at 

 the same time into a hard, spongy mass, with a semifused as- 

 pect, resembling coke. In this state, it is excessively incom- 

 bustible ; and indeed it would be found almost impossible to 

 bum it over a spirit lamp, without pulverizing it anew. The 

 intermixture of earthy matter with the pounded coal, which, of 

 course, always takes place after the calcination of the first por- 

 tion, has the beneficial effect of diminishing this tendency to 

 concretion, and it also accelerates the combustion. 



Upon examining the incombustible residue, which consists 

 of the earthy ingredients of the coal, as there is frequently 

 some sulphate of lime in it, this substance, which possesses a 

 slight degree of solubility, may be dissolved out by boiling the 

 ashes in distilled water; the clear liquid must then be separat- 

 ed and evaporated to dryness, and the weight of the residue 

 ascertained. To determine the constituents of the portion 

 which remains insoluble in water, the same method of analysis 



