ON THE ASSA,T[ING OF COALS BY THE BLOWPIPE. 215 



capsule in wliiGh the weighings are performed, and its weight ascer- 

 tained. In transferring the coal from one vessel to the othex, the 

 larger pieces should be removed by a pair of fine brass forceps, and the 

 little particles or dust afterAvards swept into the weighing capsule by 

 means of the camel' s-hair pencil or small colour-brush belonging to 

 the balance case. The weighing capsule should also be placed in the 

 centre of a half-sheet of glazed writing paper, to prevent the risk of 

 any accidental loss during the transference. After the weighing, the 

 operation must always be repeated to ensure that no further loss of 

 weight occur. In place of the blowpipe-lamp^ the spirit-lamp may be 

 employed for this operation, but with the former, there is less danger 

 of the heat becoming too high. By holding a slip of glass for an in- 

 stant, every now and then, over the capsule, it will soon he seen when 

 the moisture ceases to be given off. It should be remarked, that some 

 anthracites decrepitate slightly when thus treated, in which case the 

 porcelain capsule must be covered with a small watch-glass. 



Estimation^ ^c, of Coke : — In this operation, the small crucible is 

 employed. Particles are detached from the assay specimen as before, 

 by the cutting pliers, and about 100 or 150 milligrammes taken for the 

 experiment. The weighing is performed in the crucible itself, this 

 being placed in the little weighing-capsule, with its handle-support 

 projecting over the side. The crucible, with its cover on, is then 

 brought gradually before the blowpipe to a red heat. The escaping 

 gases will take fire and burn for a few seconds on the outside of the 

 vessel, and a small amount of carbonaceous matter may be deposited 

 upon the cover. This, however, rapidly burns off on the heat being 

 continued ; and as soon as it disappears, the crucible is to be withdrawn 

 from the flame, cooled quickly, and weighed always with its cover on. 

 The loss, minus the weight of moisture as ascertained in a previous ex- 

 periment, gives the amount of volatile or gaseous matter. The residue 

 is the coke and its contained ash. The coke should be examined by a 

 magnifying glass, and its general aspect and characters noted down^ 

 As already explained, some coals yield a swollen, semi-fused, and. 

 agglutinated coke, with a mamillated surface and metalloidal aspect. 

 Others produce a slightly fritted; and partially agglutinated coke ;. 

 others again, an unfused coke retaining the form of the coal fragments 

 subjected to the assay ; others, a pulverulent, or a strongly-soiling 

 coke, and so on. It is sometimes desirable to take the specific gravity 

 of the coke, 



Estitnation. of Ash : — The platinum capsule is employed for this 

 operation. The coal must be reduced to a coarse powder, and about 



