Zinc DesilvcrizaliiriK 87 



t;mk iron, there does not tippear to be any reasou why it 

 sliould not be of donble the size, except the uneertainty of 

 being able to purchase the supply of lead to work continuously. 

 With an uncertain sujiply, it is better to multiioly furnaces, as 

 a small amount can be better and more economically treated in 

 a small than in a large furnaoa. There is a point, however, be- 

 yond which it will not be profitable to increase the size, and this 

 will be the quantity that can be held by the kettles. The limit 

 in the kettles will evidently be that at which a man can no longer 

 work the kettle conveniently. • 



The fireplace at Cheltenham is 2 feet 3 inches wide and 5 feet 6 

 inches long. The grate is 12 inches below the bridge; the bridge 

 is 2 feet 2 inches below the roof, 1 foot 6 inches above the hearth, 

 and 2 feet 10 inches wide. The hearth is made of a cast iron 

 basin which is 15 feet 5 inches long, 9 feet 6 inches wide in the 

 middle, and 5 feet 3 inches at each end, 2 feet 4 inches deep, and 

 I4 inches thick. It weighs 8 tons, and is calculated to hold 25 tons 

 of lead. At Cheltenham, the pan forming the bottom of the fur- 

 nace is cast in one piece. At the Germania works, it is cast in 

 three pieces and bolted together. This latter method is the cheap- 

 est; but if any of the bolts become loosened, there will be a loss of 

 lead, to avoid which the works at Cheltenham had the pan made 

 in one casting. At the Pennsylvania Lead Works, the pan is made 

 of tank iron about one quarter of an inch thick, which is riveted. 

 It is now proposed to water-jacket all of these furnaces, which 

 will both reduce the quantity of repairs to be made to them, 

 and shorten the time spent upon them. The doors of this 

 furnace are counterpoised with pigs of lead, so that they can be 

 very easily moved. They are beveled and fit into a slot, so that 

 when they are closed and luted they are hermetically sealed. 



The hearth proper is built on the iron pan bottom. It 

 is made of fire-brick laid in the form of an inverted arch, 

 placed on a bed of coke next the pan, which is covered with 

 a layer of brasque. The side walls resting on it bear against 

 projections on the rim of the sides of the pan. These precautions 

 are necessary in all iron pan hearths, to prevent the rising of the 

 hearth from the lead penetrating below it, and breaking it up. 

 Notwithstanding all the precautions taken against it, this 

 9;Ccident, which causes great inconvenience and loss, happens 



