On hardening and temperin® Steel. 149 
thaking ule of quickfilver inftead of water, I have never re- 
fumed ‘the experiment. As methods are now well known 
by which water may-be cooled below the freezing pcint, 
even by the fire-fide, and at an eafy expence; fome one who 
has time may perhaps think the experiment worth repeat- 
ing: it might caft fome light upon the fubjeé of hardening 
fteel, and lead to fome ufeful refults. 
The difh J employ for tempering is very fimple (A fig. 3, 
Plate IV.) and may be of any fize, with a proportioned 
handle. It is made of plate-iron, with an edge turned up 
on every fide a fufficient height to hold tallow or oil enough 
to cover the pieces to be tempered. The corners are nipped 
together, and then folded up againft the fides, as reprefented 
in the figure; by which means they are prevented from let- 
ting out the oil. | 
The other pan or difh B, turned up on three fides only, is 
ufed to lay pieces intended. to be hardened: a cover is of 
advantage where the pieces are intended to come out clean’ 
and bright, as it more perfeétly defends them from the air, 
and of courfe prevents oxidation from taking place. By this 
inftrument the work, though ever fo {mall or flender, may” 
‘be brought out of the fire and dropped into the water with 
very little lofs of heat. It ought to be made of ftronger’ 
plate-iron than is neceflary for the other pan, and the cor- 
ners cut out fo that the fides may bend up moré fquare. 
They need not be folded as in the other, not being intended 
to hold any liquid fubftance. Such articles as fmall drills, 
pendulum and other {mall {prings need not be dropped into’ 
water, but only made to pafs through the air by tofling them 
eut and letting them fall to the ground, which will make 
them hard enough for moft purpofes. 
Small drills may be hardened by holding their points in the 
flame of a candle, and, when fufficiently hot, fuddenly pluck- 
ing them out: the air will harden them; and they may 
then be tempered, by taking a little of the tallow upon their 
cay and then paffing them through the flame at about 
“W.2 . half 
