PREPARATION OF POTASSIUM. 



441 



engaged. The crucible is then withdrawn from the fire, and is 

 found to contain a black mass, which is the mixture of char- 

 coal and carbonate of potash, known as black flux. It is re- 

 duced to powder, while still warm, and immediately mixed 

 with about ten ounces of wood-charcoal in small pieces, or in a 

 coarse powder, from which the dust has been separated by a 

 sieve. The use of this additional charcoal is to act as a sponge, 

 and absorb the potash when liquefied by heat. The mixture 

 is introduced into a bottle of wrought iron, and a mercury 

 bottle (page 244) answers well for the purpose, but must be 

 heated to redness before hand, to expel a little mercury that re- 

 mains in it. The mouth of the bottle is enlarged a little by 

 means of a round file, and a straight iron tube of 4 or 5 

 inches in length fitted into the opening, by grinding. The 

 bottle and tube thus form a retort, which is supported horizon- 



FIG. 45. 



tally in a brick furnace, as represented (Fig. 45) in which a is the 

 iron bottle resting upon two bars of iron o o, to which it may 

 also be firmly bound by iron wire. These bars cross the fur- 

 nace at a height of 5 or 6 inches above the grate-bars. A 

 mixture of equal parts of coal and coke makes an excellent 

 fuel for this furnace. The tube b of the bottle projects through 



