FOR MEASURING THE EXPANSION OF SOLIDS. 
277 
found by boiling in mercury to be equal ; the arc in both cases being with the 
platinum bar 1° 20' = .0116. They were marked IV and V. 
IV was adjusted with the platinum bar. An ingot of silver, which had been 
refined by cupellation, weighing about 35lbs., was placed in a black-lead cruci- 
ble in a wind-furnace. When somewhat more than three-fourths were melted, 
the register, previously heated to a dull red, was plunged into it as before, and 
held down for ten minutes. When lifted out its surface was found perfectly 
good, and the few adhering globules of metal were easily removed. When 
cool the scale was applied, and the arc found to be 4° 10' = expansion .0363. 
Temperature of the air 65°. 
Exp. 13. The iron bar was placed in the register V, and having been pre- 
viously heated was plunged into the same pot of metal. The silver at first set 
about the black-lead and adhered to it in a large lump. At the expiration of 
ten minutes this was just melted off, and the instrument was raised out of the 
crucible in a perfectly clean state. When cool the arc measured was 7° 24' == 
expansion .0645. 
Exp. 1 4. I made several attempts at the Royal Institution to ascertain the 
melting point of cast iron ; but owing to the large quantity of the metal neces- 
sary ; to the difficulty of keeping the temperature steady by constant feeding ; 
and to the failure of crucibles, — I did not succeed. I am under obligation to 
Mr. Parker of Argyle Street, for the readiness with which he afforded me every 
facility of performing the experiment at his foundry. 
I selected a new register for the occasion, which was marked I. Its rate of 
expansion was not determined till after the experiment. A crucible was pre- 
pared capable of containing about 35lbs. of the metal. It was filled with 
pieces of the best grey iron, and placed in a powerful wind-furnace, which ad- 
mitted of the operator standing immediately above the crucible with complete 
command over it. When the metal was melted, the crucible was lifted from 
the furnace, and the dross skimmed off its surface. It was then replaced ; a 
lump of the same iron was thrown into it, and the register, previously heated 
red hot, was immersed in the fluid to about the same depth as in the former 
experiments. It was kept in this situation by means of a pair of tongs for ten 
minutes, and afterwards gently lifted out and laid upon hot sand. A thin 
scale of iron adhered to the black lead, which when cold was easily removed, 
