Intelligence and Miscellarieous Articles. 



395 



drilled through its bottom. This crucible when placed upon the top 

 of the other constitutes the muffle, and of course resembles in shape 

 a skittle. To cupel with this apparatus, the lower crucible is nearly 

 filled with clean sand, set upon the bars of the grate in the centre of 

 the furnace, and brought to a low red heat. The cupel containing 

 the lead and the alloy is then placed upon the sand and immediately 

 covered by the other crucible, taking care that the notch in its side 

 shall be opposite to, and correspond with the furnace-door; more 

 fuel is added, during which it is well to cover the hole in the top 

 of the muffle with a crucible lid, in order to prevent the admission 

 of dirt. When the muffle has become throughout of a bright red 

 heat, the furnace-door is thrown open, and the ignited fuel gently 

 moved aside, so as to permit a view of the side opening in the 

 muffle. The current of air which is thus established through the 

 muffle instantly causes rapid oxidation of the lead, and this may be 

 regulated at pleasure by closing the door more or less. If from 

 the fuel falling down any difficulty should be experienced in main- 

 taining a free passage for the air, a portion of a porcelain tube or a 

 gun-barrel may be passed through the furnace-door to within an 

 inch of the muffle ; but this proceeding is generally rendered quite 

 unnecessary by taking care to place some large pieces of coke im- 

 mediately around the door of the furnace. 



In many cases it will be found advantageous to convert the lower 

 crucible itself into the cupel by first half-filling it with sand and 

 then ramming in pounded bone-earth. I have found the above me- 

 thod to possess the following advantages : — In the first place, the 

 crucibles may be maintained at a much higher temperature than can 

 be readily obtained when the ordinary mufile is used, while the de- 

 gree of heat and the quantity of air admitted may be regulated with 

 the greatest nicety. Secondly, owing to the greater draught of air, 

 the oxidation of the lead is more quickly effected ; and lastly, by 

 looking through an opening in the furnace cover, the operation may 

 be watched from first to last. 



Fig. 2. 



L_. 



Fig. 2. a B black lead crucibles. C the upper opening. D the lower opening. 

 E the cupel. The dotted semicircle represents the position of the furnace-door. 



