276 
MR. DANIELL ON A NEW REGISTER-PYROMETER 
About OOlbs. of fine gold were weighed, and one of the ingots was cut into ten 
pieces for the purpose of gradually feeding the crucible, and keeping the tem- 
perature down to the true melting point during the observation. The remainder 
was melted in a black-lead crucible in a wind-furnace. When just fused, one 
of the pieces was thrown in, and the melted metal immediately congealed upon 
the surface. The register, which had been slowly heated in another crucible to 
a dull red, was then taken up with a pair of tongs and plunged perpendicularly 
into the gold about two-thirds of its height. In this situation it was kept ten 
minutes, and during the time two more lumps of the metal were thrown in. It 
was then carefully lifted out and set apart to cool. Its surface was perfectly clean, 
only a few small globules adhering to it, which were easily removed. I may 
here remark that stirrers of the black-lead earthenware are constantly used at 
the Mint for agitating the melted gold. The arc measured from this experiment 
was 6° 10', equivalent to an expansion of .0537. Temperature of the air about 65°. 
Exp. 9. The register III was fitted with the iron bar, and also heated to a 
dull red. The temperature of the melted gold was prevented from rising by 
constant feeding with the pieces ; the crucible being never left without some 
portion unmelted. It was then plunged beneath the surface of the metal as in 
the preceding experiment, and held in that situation for ten minutes. The arc 
measured was 9° 2', indicating an expansion of .0787. 
Exp. 1 0 . The rates of expansion of the two last registers were determined by 
boiling them for ten minutes each in mercury. The results were as follow : 
Arc. Expansion. 
II with the platinum bar 1°.50 = .0159 
III with the iron bar 2°.38 = .0229 
Exp. 11 . About 50lbs. of pure silver were melted in a black-lead pot: a 
little scum floated upon the surface, which appeared at first like drops of oil 
upon a basin of water. I was afterwards informed that the metal had been 
refined with nitre, and the dross was owing to the action of a little remaining 
potash upon the crucible. Two registers had been prepared for the platinum 
and iron bars; but the observations were lost from the same action upon their 
substance. They were so deeply corroded in a line which corresponded with 
the level of the fluid metal, as to render it impossible to apply the scale, with 
any certainty, to their surfaces. 
Exp. 12. Two new registers were selected, whose rate of expansion was 
