465 
Process for Refining Lead . 
This frame is something larger than the elliptical hole in 
the bottom of the furnace. 
Figs. 2 and 3, plan and section of the test; m the part 
which contains the lead to be refined, n breast of the 
test, oo small gutters or channels through which the 
litharge flows, p a semi-eliptical hole for the litharge 
to fall through from the gutters upon the area of the re- 
finery. 
These drawings and references will be sufficient to 
make the description of the furnace, &c. clearly under- 
stood. 
Of the Test or Cupel. 
A good test is of the first importance in refining; the 
method of constructing one I shall endeavour to point 
out. Six parts of well burnt bone ashes and one part of 
good fern ashes are to be well mixed, sifted through a 
sieve, (the spaces in which are about one-eighth of an 
inch square,) and moistened to about the same degree 
the founders use their sand. The iron frame is to be 
laid on the floor and made steady, with wedges under its 
rim ; about two inches in thickness of the ashes are to be 
equally spread over the bottom, and with an iron beater, 
such as used by the founders, equally rammed between 
the cross bars ; the frame is to be again filled and rammed 
all over, beginning at the circumference and working 
spiral ways until finished in the centre, the filling and 
ramming to be repeated until the frame is completely 
full; an excavation to contain the lead is made as ex- 
pressed in the plan, with a sharp spade about five inches 
square, the edges dressed with a long-bladed knife; 
a semi-eliptical hole, as at p, is to be cut through 
the breast. Having proceeded so far, the test is to be 
turned on its side and dressed from all superfluous 
ashes adhering to the bottom, taking care that none 
Yol. it. 3 M 
