210 ON THE ASSAYING OF COALS BY THE BLOWPIPE. 



composition : — Carbon, 92|^, Hydrogen 3^, Oxygen {with trace of 

 Nitrogen) 4. All yield, an amount of coke equal to or exceeding 89 

 per cent. The coke is frequently pulverulent, never agglutinated. 



The comportment of anthracite before the blovrpipe has not hitherto 

 been given in detail. It is as follows : — Per se, the assay quickly 

 loses its metallic brilliancy. After continued ignition, small white 

 specks of ash appear on its edges. In borax it dissolves very slowly, 

 vdth constant escape of bubbles. It is not attacked by salt of phos- 

 phorus ; the assay works to the top of the bead and slowly burns 

 away. In carbonate of soda, it effervesces, scintillates, and turns 

 rapidly in the bead ; and the soda is gradually absorbed. In the bulb 

 tube a little water is always given off, but without any trace of bitumi- 

 nous matter. 



As regards their geological position, the true anthracites belong 

 chiefly to the middle portion of the Palaeozoic series, below the Carboni- 

 ferous formation ; or othervidse, they constitute the under portion of 

 the coal measures. Frequently also, anthracites occur in the vicinity 

 of erupted rocks, and amongst metamorphic strata, as manifest altera- 

 tions of ordinary coal. 



2. Anthi'acitic Coals. — These are often confounded with the true 

 anthracites, into which indeed, as already stated, they gradually merge. 

 Normally, they differ from the true anthracites in being non-conductors 

 of electricity, in burning more easily and with a very evident yellow 

 flame, in yielding a small quantity of bituminous matter when heated 

 in a tube closed at one end, and in furnishing an amount of coke below 

 80 per cent. The coke is also in general more or less agglutinated, 

 although it never presents the fused, mamillated appearance of that 

 obtained from caking coal. The mean composition, ash and moisture 

 deducted, may be represented as follows : — Carbon 89|^, Hydrogen 5, 

 Oxygen (with trace of Nitrogen) 5| ; or Carbon 89, Hydrogen 5, 

 Oxygen (with trace of Nitrogen) 6. 



3. Caking Coals. — These are often termed, technically, " Fat coals." 

 They constitute the type-series of the coals, properly so called* All 

 yield a fused and mamillated coke, varying in amount from 65 to 70 

 percent, Sp, gr.=1.27-1.32. Commonly mixed with thin layers of 

 strongly soiling "mineral charcoal" or fibrous anthracite. Mean com- 

 position (ash and moisture excluded) : Carbon 87-9, Hydrogen 5.1, 

 Oxygen (with nitrogen) 7-0. 



4. Cannel or Gas Coals. — These coals, at least in normal specimens, 

 do not fuse or " cake" in the fire. They give off a large amount of 

 volatile matter, frequently more than half their weight ; hence their 



