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



of coals, an application peculiarly fitted to it; since, in travelling, 

 and at other times when only the blowpipe apparatus can be con- 

 veniently made use of, determinations of the kind in question 

 are often desirable. Having had some experience in the use of 

 the instrument, I have attempted to supply this deficiency ; and 

 thinking the subject of sufficient interest to obtain a place in the 

 pages of the Philosophical jMagazine, I have embodied in the 

 present paper the results of my investigations. The subject may 

 be conveniently considered under the following heads: — (1) Coal 

 in its different aspects; (2) Instruments and appliances; (3) Ope- 

 rations. 



§ 1 . Varieties of Coal. 



Without attending to minor distinctions or points of merely 

 local value, we may arrange all varieties of coal, so far as regards 

 practical purposes, under the following subdivisions : — 



1. Anthracites. 



2. Anthracitic or Dry Coals. 



3. Caking or Pat Coals. 



4. Cannel or Gas Coals. 



5. Brown Coals or Lignites. 



These varieties pass by almost insensible transitions into one 

 another. Thus, the cannel coals are related to the lignites by 

 the different kinds of jet, some of which are referable to the one 

 and some to the other subdivision. Between the caking and the 

 cannel coals there are also various links ; whilst the anthracitic 

 or dry coals, on the other hand, — passing by excess of bitumen 

 into the caking coals, and by a diminution of bituminous matter 

 into the anthi'acites — serve to connect the first and third divi- 

 sions. The typical or normal specimens of each of these five 

 varieties, however, are sufficiently well marked. 



1. Anthracites. — The true or normal anthracites possess a 

 brilliant sub-metallic lustre, a degree of hardness varying from 

 3"0 to 3*25*, and a specific gravity of at least 1'33. A speci- 

 men from Pennsylvania gave 1'51 ; another specimen, 1"44; 

 one from the department of the Isere in Prance, i*56; and three 

 from Wales yielded respectively 1"33, 1'37, 1-34. It should be 

 stated, however, that many of the Welsh specimens belong 

 strictly to the division of anthracitic coals, rather than to that of 

 the true anthracites. The normal anthracites exhibit also a 

 black or greyish-black streak ; and all are good conductors of 

 electricity. The latter character may be conveniently shown by 



* Hausmann in his Handbuch der Mineralogie, gives 2"5 as the extreme 

 hardness of all coals ; but this is evidently erroneous, as many specimens, 

 not only of anthracite, but of common and cannel coals, scratch calcareous 

 spar. 



