Prof. Chapman on the Assaying of Coals by the Blowpipe. 441 



as already directed, be emplo}red, a temperature sufficiently high 

 to bum off the carbon from most coals is in this manner attain- 

 able. The lid of the capsule must be placed above the coal- 

 powder until combustion cease, that is to say, until the gaseous 

 products be driven off, and only the uninflammable carbon and 

 ash remain ; as, otherwise, a portion of the powder might very 

 easily be lost. Some of the anthracites also decrepitate on the 

 first application of the flame, although rarely perhaps when the 

 coal is in the form of powder ; still it is advisable in all cases to 

 keep the assay covered until the flame cease. During the after- 

 combustion, the powder or small particles must be gently stirred 

 and carefully turned over, and if agglutinated, broken down by 

 a light steel spatula, or better still, by a small spatula of pla- 

 tinun*, made by inserting a strip of stout ])latinum foil (an inch 

 long) into one of the ivory or wooden handles intended pj™ 4 

 to hold platinum spoons. These handles are quite 4r 

 useless for the latter purpose, or at least are far in- 

 ferior to the steel forceps described above. With the 

 forceps, for example, the spoons can be taken up and 

 disengaged in an instant, and without the intervention 

 of the right hand. Whilst the spoons, also, are still 

 red-hot, the forceps may be laid down without the 

 spoons coming in contact with the table. Figure 4 

 shows the form and size of the spatula that I employ. 

 A is the ivory handle ; C the piece of stout platinum 

 foil fitting into a slit in A ; and B the metal ring 

 which keeps the two together. The platinum, it 

 should be remarked, must be sufficiently stoat to 

 resist bending; and its point must be kept quite 

 bright and smooth by occasional polishing on a smooth 

 part of the agate mortar which always accompanies the 

 blowpipe. If by the method of procedure just de- 

 scribed, the carbonaceous matter be not finally burnt 

 off, the flame of the blowpipe — using the oil-lamp, or 

 spirit-lamp with the wick well up — may be employed 

 to accelerate the process. The operator, however, must be care- 

 ful to keep the capsule inclined away from the flame, in order 

 to avoid the loss of any portion of the fine light ash. Finally, 

 when the ash ceases to exhibit in any of its parts a black colour, 

 the lid of the capsule is to be cautiously replaced, and the whole 

 cooled and weighed *, 



Nature of the Ash. — As already remarked, the ash or inorganic 



* If tlie ash be very ferruginous, the results thus obtained, to be exact, 

 will require correction : the original iron pyrites of the coal being weighed 

 as ses(|uioxi(le of iron. In ordinary cases, however, — in assays as distin- 

 guished from analyses,— this may be fairly neglected. 



When, also, the ash is calcareous, and in considerable quantity, it should 

 Phil. Mag. S. 4. Vol. 15. No. 102. June I808. 2 G 



