FOR MEASURING THE EXPANSION OF SOLIDS. 
451 
holes. The register, with the wrought iron was then taken out. The bar of 
the latter was found perfect, without any signs of oxidation or fusion. 
The arc measured of the cast iron w T as .... 9° 47' 
The arc of the wrought iron 7° 56' 
I had some reason to think that the register, with the wrought iron bar, had 
not been exposed so fully to the heat as that with the cast iron : for, although 
placed slightly in advance of the latter towards the body of the furnace, it was 
not raised so high from the floor of the flue, which probably had a cooling in- 
fluence; and as the flame was drawn upwards, it must have struck with greater 
force upon the higher register. I therefore replaced the wrought-iron bar in 
the register, and put it exactly in the position previously occupied by the cast 
iron ; it was then covered with charcoal, and the fire urged to the utmost. 
At the expiration of twenty minutes it was removed : the bar was found unin- 
jured, with a white metallic lustre, except over the apertures, where it was blue, 
and perfectly free from oxide. The arc now, however, measured 11° 16'. 
Now from these experiments there are four ways of approximately deter- 
mining the temperature of melting cast iron. 
1st. By taking the expansion of cast iron to its melting point, and calcu- 
lating from the expansion for 150° to the boiling point of water, upon the sup- 
position that the same rate is maintained, and adding the initial temperature 
of 60°, we obtain 3096°. 
2ndly. By calculating from the expansion of the same bar for 600° to the 
boiling point of mercury, supposed equal, we obtain 2489°. 
3rdly. By assuming the expansion of a bar of wrought iron, at the point of 
melting cast iron, and calculating from the expansion of the same bar for 150° 
to the boiling point of water, we obtain 295 /°. 
4thly. By calculating from the expansion of the same bar for 600° to the 
boiling point of mercury, supposed equal, we obtain 2533°. 
It is remarkable that the mean of these four determinations is 2768° ; for it 
will be remembered that the corrected temperature, which I deduced from the 
expansion of a platinum bar plunged into melting cast iron, was 2786°. 
It may be observed, that in both cast iron and wrought iron, the calculation 
from the rate of expansion to the boiling point of water gives a temperature 
higher than the true ; and that, in both, the calculation from the point of boil- 
