an 



Method o£ 

 blowing, &c« 



HEFINING OF LEAD. 



Gutter for the 

 litharge. 



Ixt/lrudUoDS. 



raked off through the paffage left for the litharge, by means of 

 a wooden rake about a foot long, with an iron handle of fuf- 

 ficient length to reacli every part of the bath. 



When the lead has been feveral times fkimmed, and begins 

 to become red, the bellows muft be fet into action, gently at 

 firft, and afterwards more ftrongly. Theirnozles muft be fo 

 difpofed that the blaft may be direded towards the center of 

 the bath, and in order that the wind may be urged upon the 

 iurface of the metal, each nozle muft have afmall round plate 

 of iron adapted to it. Thefe fmall flaps or valves, called 

 papillons (flies or butterflies) are u fed in the German fineries. 

 They have an hinge at top, and at every ftroke they rife about 

 half way from their perpendicular potition towards the level, 

 fo that by reflecling the air downwards upon the lead, they 

 haften its oxidation. 



When all the drofs has been removed, and the lead is of a 

 good red heat and covered with litharge, a little gutter muft 

 be made, with an hook appropriated for this purpofe, in the 

 iand of the cupel. This muft be carefully done until the bot- 

 tom of the gutter anfwers to (he level of the bath. The li- 

 tharge driven by the blaft of the bellows will flow out of this 

 pafl'age, and fall upon the hearth of the foundery. 



When the operator perceives that only a fmall quantity of 

 litharge remains near the gutter, he will flop its efcape with a 

 fmall quantity of moiftened aflies ; but as foon as the lead fliall 

 be again covered with oxide, the paflage muft be opened and 

 made deeper as the quantity of matter becomes depreffed ; 

 taking care that no lead efcapes, particularly towards the end 

 of the operation, as it would carry along with it a large por- 

 tion of filver which would be loft. 



In this manner the procefs is to be carried on until the fur- 

 face of the filver exhibits thofe flaflies which are called the' 

 brightening, taking care to raife the fire in proportion to the' 

 diminution of the bath, particularly towards the end, when 

 the filver is colleded; and as this metal is much Qiore difficult* 

 to be kept in fufion than its fmall alloy of lead, the refining 

 will be imperfefl, unlefs the temperature be raifed, and in-' 

 ftead of about one twentieth of lead, which the filver ulually' 

 retains in the German method, it will remain much mor« 

 highly charged. This would render it more difficult to be 

 treated in the tecond operation, called the filver refining, or^ 

 fay ttie Gerniansyi/rer brenen, by which it is rendered pure. 



5 Thofe 



