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



when subjected to the pressure of the fingers. I Fig. 3. 

 give a figure of the kind that I employ, because it 

 is much more convenient than the forceps commonly 

 put up in blowpipe cases ; or indeed, than any that 

 I have found described in works on the blowpipe, or 

 in the catalogues of the instrument makers. In 

 using these tongs, the left-hand need only be em- 

 ployed. They open by the pressure of the forefinger 

 and thumb upon their sides. (4) A balance. The 

 most convenient kind of balance for use in these ope- 

 rations is that first contrived by Lingke of Freiberg, 

 for Plattner's assaying experiments. It is figured 

 and described in detail in the for|.'th edition of Platt- 

 ner's Probirkunst mit deni Lothrohre. This balance 

 takes to pieces, and packs with its weights, forceps, 

 . &c., into receptacles cut for it in a small box of pear- 

 tree wood, the size of a thin octavo volume. It can 

 be fitted up ready for use in the course of a few 

 minutes ; and its delicacy is very great. That which 

 I employ, when loaded with 3 grammes, a greater 

 weight than it is ever required to carry, turns readily 

 with less than half a milligramme, or the 0-0077th 

 of a grain. It is convenient to have counterpoises 

 for the platinum vessels described above, as the 

 weights belonging to the balance only range from a 

 gramme downwards. A small platinum capsule forms the best 

 kind of counterpoise. It can be trimmed down by a knife or 

 pair of scissors, until brought, after repeated trials, to the proper 

 weight. In spare places in the box containing the balance that 

 I use, I have cut out receptacles for the two platinum vessels 

 and their counterpoises, and I recommend other operators to do 

 the same, because these platinum vessels are of frequent use in 

 various experiments unconnected with the present inquiry; as 

 in ascertaining the amount of water in minerals, and so forth. 



§ 3. Operations. 



In the examination of coals, the following operations are 

 necessary : — (1) The estimation of the water or hygrometric 

 moisture present in the coal ; (2) the estimation and examina- 

 tion of the coke yielded by the coal ; (3) the estimation and 

 examination of the ash or inorganic matters present in the coal ; 

 and (4) the estimation of the sulphur, chiefly contained in the 

 coal as Fe S^. 



To these might be added, the determination of the heating 

 powers of the coal ; but this operation, at all times one of more 

 or less uncertainty, cannot be performed by the blowpipe in a 



