214 ON THE ASSAYING OF COALS BY THE BLOWPIPE. 



To these might he added, the determination of the heating powers 

 of the coal ; but this operation, at all times one of more or less uncer- 

 tainty, cannot be performed by the blowpipe in a satisfactory manner. 

 This, however, is really of little consequence, as apart from the doubt- 

 ful character of the experiment even when conducted on the large 

 scale, the relative heating powers of different samples of coal may 

 generally be estimated sufficiently near for practical purposes by a 

 comparison of the amount of coke, ash, and moisture. The litharge 

 test commonly resorted to for the determination of the calorific power 

 of coals, when properly considered, is of very little actual value. Take, 

 for example, the respective results furnished by good wood-charcoal 

 and ordinary coke. These results are closely alike or rather in favour 

 of the charcoal ; and yet experience abundantly proves the stronger 

 heating powers of the coke. It is impossible to raise the temperature 

 of a furnace with charcoal to anything like the same degree as that ob- 

 tainable by the employment of coke. Besides which, in practice, it is 

 not as a general rule, the absolute calorific powers of a coal that con- 

 stitute its availability for ordinary operations, because a coal^ — such, 

 for instance, as a brown coal rich in bitumen— may possess heating 

 powers of considerable amount, but only of short duration : and in 

 cases of this kind, the litharge test becomes again unsatisfactory. 

 Thus the lignites of the department of the Basse Alpes, already alluded 

 to, yield with litharge from 25 to 26 of lead ; whilst many caking 

 coals, practically of much higher heating powers, yield scarcely a 

 greater amount. For these reasons, whilst seeking to discover a satis- 

 factory method of ascertaining directly by the blowpipe the heating 

 power of coals, I leave the subject out of consideration in the present 

 paper. 



Estimation of Moisture : — This operation is one of extreme sim- 

 plicity. Some slight care, however, is required, to prevent other 

 volatile matters from being driven off during the expulsion of the 

 hygrometric moisture. Seven or eight small particles, weighing to- 

 gether from 100 to 150 milligrammes, are to be detached from the 

 assay-specimen by means of the cutting pliers, and carefully weighed. 

 They are then to be transferred to a porcelain capsule with thick bottom, 

 and strongly heated for four or five minutes on the support attached to 

 the blowpipe lamp : the unaided flame of the lamp being alone employ- 

 ed for this purpose. It is advisable to place in the capsule at the same 

 time, a small strip of filtering or white blotting paper, the charring of 

 which will give indications of the temperature becoming too high. 

 The coal, whilst still warm, is then to be transferred to the little brass 



