218 ON THE ASSAYING OF COALS BY THE BLOWPIPE. 



added to the carbonate of soda, in order to promote the sokition of the 

 assay, and the more ready formation of an alkaUne sulphide. If oxide 

 of manganese be present in the ash, by fusion with carbonate of soda 

 and a little borax, we obtain the well known bluish-green manganate 

 of soda, technically termed a turquoise-enamel. 



Estimation of Sulphur : — The method of detecting the presence of 

 sulphur in coal, is the same as that just pointed out for the detection of 

 sulphate of lime in the ash. The actual estimation of the sulphur is a 

 much more troublesome operation. A process given by Berthier, in his 

 Traite des Essais par la voie seche, consists in boiling the ferruginous 

 ash in hydrochloric acid, which dissolves out the sesqui-oxide of iron, 

 and then calculating the sulphur from the loss. One hundred parts, 

 for example, of sesqui-oxiJe of iron correspond to 70.03 of metallic 

 iron; and hence to 150.24 of iron pyrites, or to SO. 21 of sulphur. 

 But this method, besides requiring a larger quantity of ash than can 

 be conveniently prepared in these blowpipe examinations, exacts that 

 the other portion of the ash be not attackable by the acid, a condition 

 which of course does not obtain in the case of calcareous ashes. For 

 this reason, the process recommended by Rose and other chemists is 

 preferable, although somewhat beyond the range of blowpipe examina- 

 tions. About 200 milligrammes of the coal in fine powder are to be 

 intimately mixed with 8 parts of nitrate of potash, 4 of carbonate of 

 potash, and 16 of common salt, and the mixture fused in a platinum 

 crucible over the spirit-lamp, with the wick well pulled up, or, better 

 still, over a double current or Berzeliu'slamp. The fused mass is then 

 to be dissolved out in boiling water, to which a few drops of hydrochloric 

 acid have been added, and the sulphuric acid thrown down by chloride 

 of barium. By dividing the precipitate thus obtained (after filtration, 

 careful washing, and ignition,) by 7.25, we get the amount of sulphur. 

 As the above process, although simple enough in the performance, 

 is scarcely available when the operator is away from home, I have at- 

 tempted to hit upon a more ready method, and one more properly 

 within the legitimate pale of blowpipe experimentation, of ascertain- 

 ing approximatively the amount of sulphur in coal samples. After 

 various trials, I have found the following process sufficiently exact for 

 all ordinary cases, because, as a general rule, we merely require to 

 know here, if the coal under examination be slightly, moderately, or 

 highly sulphurous. It consists essentially in comparing the intensity 

 of the stain produced on silver foil by an alkaline sulphide of known 

 composition, with that formed by an alkaline sulphide obtained from 

 the assay-coal. For this purpose, mixtures must first be made of a 



