262 Mr. Daniell on a New Regisler-Pj/romctcr 



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 I'e- 

 moved: the bar was found uninjured, with a white metallic 

 lustre, except over the apertures, where it was blue, and per- 

 fectly free from oxide. The arc now, however, measured 

 11° 16'. 



Now from these experiments there are four ways of ap- 

 proximately determining the temperature of melting cast-iron. 



1st. By taking the expansion of cast-iron to its melting 

 point, and calculating from the expansion for 150° to the 

 boiling point of water, upon the supposition 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°. 



Srdly. By assuming the expansion of a bar of wrought-iron, 

 at the point of melting cast-iron, and calculating from the ex- 

 pansion of the same bar for 150° to the boihng point of water, 

 we obtain 2957°. 



4-thly. By calculating from the expansion of the same bar 

 for 600° to the boiling point of mercury, supposed equal, we 

 obtain 2533°. 



It is remai'kable that the mean of these four determinations 

 is 2768° ; for it will be remembered that the corrected tem- 

 perature, which 1 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 temjjeratux'e higher than the true ; and 

 that, in both, the calculation from the point of boiling mer- 

 cury affords a result lower than the true. This might afford 

 some grounds for conjecturing that, although the rate of ex- 

 pansion evidently increases beyond the temperature of boiling 

 water, it does not continue to increase to the end ; but there 

 is another inference from the fact, which I am rather inclined 

 to adopt. 



In calculating the temperature of melting cast-iron, from 

 the expansion of the platinum bar, I applied a correction, upon 

 the supposition that the same rate of increase of expansion 

 which was exhibited by platinum between the boiling points 

 of water and mercury continued to the higher degrees; whereas 

 there is great reason to suppose that the rate must be an in- 

 creasing one; and, although this might not sensibly affect the 

 final result of the comparatively low temperature of melting 



I 



