for Measuring the Expansions of Solids, Sj-c. 355 



when cold were perfectly hard and inflexible. I again heated 

 a portion of the bar to a dull red, and it crumbled to powder 

 from a slight blow with a hammer. 



Exp. 21. — It being a point of the greatest interest to 

 ascertain the maximum of expansion which took place in the 

 platinum previous to this remarkable change of structure, I 

 adjusted the original platinum bar, with which the greater part 

 of my experiments had been made, and which presented a 

 perfectly smooth surface, and was very soft and ductile, in the 

 register I. A crucible was placed in the same wind-furnace, 

 containing only a little charcoal powder, with the iron nail 

 and fragments of porcelain as test pieces. The fire was urged 

 to the utmost; and when it had been continued two hours 

 the cover was removed, and the register, previously made 

 red hot, was carefully introduced, the cover replaced, and the 

 ignited fuel heaped upon it. At the expiration of a quarter 

 of an hour it was lifted out and cautiously cooled. An ex- 

 cellent measure was obtained, and the arc determined to be 

 7" 24' = expansion 'QG^o. 



The test pieces were found in the same state as in the pre- 

 vious experiments. The platinum bar was loose in the cavity, 

 and had not altered its form ; but its surface had assumed a 

 slightly crystalline texture, and it had become very hard and 

 inflexible. 



The expansion registered would, upon the hypothesis be- 

 fore assumed of equal amounts of expansion denoting equal 

 increments of temperature, indicate a heat of 3336° ; or, add- 

 ing the initial temperature 65°, = S^Ol °. But it must be remem- 

 bered that this is probably rather the temperature at which 

 the change in the structure of the platinum took place, than 

 the utmost heat of the furnace. The latter may possibly ex- 

 ceed the degree at which the expansion of the metal ceases, 

 and at which its particles evidently form a new arrangement; 

 but this point cannot at present be determined. The coinci- 

 dence of this result with that obtained in the former series of 

 my experiments, is very remarkable. The temperature at 

 which I obtained the fusion of cast iron at that time was cal- 

 culated at 3479°, and was produced by the utmost energy of 

 an excellent wind-furnace: and this, it will be observed, is 

 within 80° of the present maximum. 



Exp. 22. — Being desirous of ascertaining whether the re- 

 gister and platinum bar had undergone any change in their 

 rates of expansion by the intense heat to which they had been 

 exposed, I again adjusted the latter in the register I, which 

 had now been once immersed in melted iron, and three times 

 subjected to the action of the wind-furnace, and boiled thenn 

 2 Z 2 for 



