Zinc Dcsih'crizntidn. 



101 



The following table covers live runs; unfortunately the lists do not 

 specif}^ how manj^ retorts were fit for further service at the end of a run : 



No. of Retorts. I II III i IV V VI 



1st Run, - 13 7 11 j 12 9 13 



2d " - . 12 10 9 10 9 12 



3d " - - 10 13 i 8 10 12 7 



4th " - , 12 15 I 12 12 15 7 



5th " - - 13 14 I 7 13 13 13 



The figures give the number of charges made in each retort. 



At Cheltenham the retorts are set in the furnace, Fig. 9, with 

 the level of the bottom below the mouth, and so inclined that the 

 syphon, Fig. 10, can draw out nearly the whole of the silver lead. 

 Some of it will remain, but this is no disadvantage, as it is not 

 lost. It is collected when the retort is broken. Its presence, 

 however, requires that a reducing temperature should always be 

 kept up in the retort, otherwise litharge would form and the 

 retort be quickly pierced. The furnace is a cube of fire-brick, 

 3 feet in size, braced in every direction with wrought iron bands 

 3 inches wide. On the top there is a round hole, li, 10 inches in 

 diameter, for the introduction of the fuel ; on the front, is an 

 opening for the neck of the retort, c, and on the back, a square 

 flue, g, leading to the chimney. The retort is introduced from 

 the bottom, The furnace has 12 grate-bars one inch square, and 

 is supported in front on masonry, i, built with two steps, each 

 of which is 18 inches high, but vertical behind. The retort is 

 supported on a pillar of brick-work, d, resting on the ground, 

 through which the grate-bars pass. It is thus in the centre of 

 the furnace and is surrounded on all sides by fuel. It costs 

 from 114 to 116 and lasts for 15 to 30 turns. When it breaks, 

 it is not because it is worn out, but because the workmen break 

 it in trying to force off the cinders attached to it. Five of 

 these furnaces were arranged in a house by themselves, about a 

 hexagonal chimney, and connected with it by the flue, g, 3 

 feet long. The sixth side of the chimney is occupied by a melt- 

 ing-furnace. Only three of the furnaces are run at a time, the 



