To enable this steam to rise regularly in the working pot, a disk-plate
is placed above the nozzle, which acts as a baffle-plate; and uniform
distribution of the steam is the result. To quicken the formation of
crystals, and thus hasten the operation, small jets of water are allowed
to play on the surface of the lead.
This, it might be thought, would make the lead set hard on the surface;
but the violent action of the steam acts in the most effectual manner
in causing the regular formation of crystals. Owing to the ebullition
caused by this action of the steam, small quantities of lead are forced
up, and set on the upper edges and cover of the pot. From time to time
the valve controlling the thin stream of water playing on the top of the
charge is closed, and the workman, opening the doors of the cover in
rotation, breaks off this solidified lead, which falls among the rest of
the charge, and instantly becomes uniformly mixed with it.
Very little practice enables an ordinary workman to judge when
two-thirds of the contents of the big pot are in crystals, and one-third
liquid; and when he sees this to be the case, instead of ladling out the
crystals ladleful by ladleful, as in the old Pattinson process, he taps
out the liquid lead by means of two pipes, controlled by valves, the
crystals being retained in the pot by means of perforated plates.
Pages:
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86