LEAD 



69 



in a fresh test, or in that employed for the concentration of the rich lead. The 

 brightening of pure silver at the moment of the separation of the last traces of lead, 

 indicates the precise period at which the operation should be terminated, and the blast 

 is then turned off, and the fire removed from the grate. The silver is now allowed 

 to set, and as soon as it has become hardened, the wedges are removed from beneath 

 the test, which is placed on the floor of the establishment. When cold, the silver 

 plate is detached from the test, and any adhering particles of bone-ash removed by 

 the aid of a wire-brush. 



A test furnace of ordinary dimensions requires for its construction about 2,000 

 common bricks, 2,000 fire-bricks, and 1$ ton of fire-clay. A furnace of this kind 

 will work off 4 pigs of lead per hour, a'nd consume 4 cwts. of coal per ton of rich 

 lead operated on. 



1351 



Figs. 1351, 1352, and 1353, represent an elevation, plan, and section of a refining 

 furnace; A, fire-place; B, ash-pit; c, fire-bridge; D, test-ring, shown in its proper 

 position ; B, flues ; F, point where blast enters ; c, pig-holes. 1 



The cost of working a ton of rich lead in the neighbourhood of Newcastle, con- 

 taining on an average 400 oz. of silver per ton, is as follows : 



t. d. 

 2-1 

 6-8 

 7-0 



Refiner's wages * 



Coals, 4 cwts. ........ 



Engine wages 1 



Coals, 5 Cwts 08-7 



Pearlash 03-5 



Bone-ash, 17'3 Ibs ! 



Repairs 5'0 



Total . 



. 10 lO'l 



1 Pig-holes are used for introducing the lead in cases in which it is not laded into the test in 

 fused state. 



