ON THE ASSAYING OF COALS BY THE BLOWPIPE. 



213 



the platinum vessel during ignition. These tongs should 

 be so constructed as to remain closed except when sub- 

 jected to the pressure of the fingers. I give a figure of 

 the kind that I employ, because it is much more con- 

 venient 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 instru- 

 ment makers. In using these tongs, the left hand need 

 only be employed. 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 

 operations, is that first contrived by Lingke of Freiburg, 

 for Plattner's assaying experiments. It is figured and 

 described in detail in the fourth edition of Plattner's 

 " Probirkunst mit detn 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 three 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 experi- 

 ments 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 examination 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^. 



