98 Zinc Desilverization. 



weight of tlie dross collected from a kettle at tlie Germania 

 works, which was polled four times, is given below. 



1st Polling, - - - 1,301 lbs. 



2d " . . - . 881 " 



3d " - - . - - 671 " 



4th " - - - . 290 " 



Total, 3,143 " 

 The crasses from all the pollings, usually amounting to from 

 1000 to 2100 lbs., are melted, at the Germania works, in a rever- 

 beratory furnace, and make common soft lead. The crasses from 

 the softening-furnace, however, make silver lead, which is treat- 

 ed by zinc. Those from refining, which at the Germania works 

 is called calcination, make soft lead of ordinary quality. 



The following table gives the quantity of skimmings for examples Nos. 

 1 and 2, page 95. 



From retining-furnace, - - - - 31,700 lbs. 



Polling-kettle, ...... 20,35:3 " 



Quantity of work lead taken from the polling-kettle, 76.25 per ct. 

 Silver contained in the market lead, per 1000 kilogrammes, 6 grammes. 



The polling-kettles at Cheltenham, are emptied by the Steitz 

 eyphon, Fig. G. 'i'o do this, it is first heated and turned over, 

 so that the funnel- end, a, is uppermost. The stop-cock, b, is then 

 turned, and melted lead ponred into the funnel. It is then 

 turned over into the furnace. The joints of this syj)hon arc 

 made of gas-pipe fittings. At first it was supposed to be neces- 

 sary to make them perfectly air-tight, but afterward it was found 

 that when sis ur eight threads of the screw were run into the 

 the fitting, the joint was lead- tight, and perfectly flexible. The 

 end of the syphon, Avhere it turns down to discharge the lead, is 

 a simjDle gas-pipe fitting, to which a handle, c, is attached for 

 convenience of moving. While the lead is not being cast, the 

 vertical arm is simply turned uj). When the car with the pig- 

 moulds is ready, the syphon is turned down, being held by the 

 handle, and is moved from one pig-moiild to the other in suc- 

 cession, as they are filled with lead. The joint is long enough to 

 allow of filling all the moulds without moving the car. 



4. Treatment of Zinc Scums. — The zinc for the liquation, after 

 eing reduced to small pieces, is distilled. This is done in 



