Prof. Chapman on the Assaying of Coals by the Blowpipe. 439 



satisfactory manner. This, however, is really of little conse- 

 quence, as apart from the doubtful 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 obtainable by the employment of 

 coke. Besides which, in practice it is not, as a general rule, 

 the absolute calorific powers of a coal that constitute its avail- 

 ability 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 Basses 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 satisfactory 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 

 simplicity. Some slight care, however, is required to prevent 

 other volatile matters from being driven off during the expulsion 

 of the hygromctric moisture. Seven or eight small particles, 

 weighing together from 100 to 150 milligrammes, are to be de- 

 tached from the assay specimen by means of the cutting pliers, 

 and carefully weighed. They are then to be transferred to a por- 

 celain 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 employed 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 

 chari-ing 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 capsule in which the weighings 

 arc ])erformed, and its weight ascertained. In transferring the 

 coal from one vessel to the other, the larger pieces should be 

 removed by a pair of fine brass forceps, and the little particles 

 or dust afterwards swept into the weighing capsule by means of 



