for Measuring the Expansions of Solids, Sfc. 353 



ratus in which ihe water was heated or the ice melted. It is 

 probable that the process which they employed, of the calori- 

 meter, was not susceptible of great accuracy ; but the discre- 

 pancy of the results from those which I obtained from the 

 metal in analogous circumstances is not great. 



Iron just melting 3164.° by the former 



2889 by pyrometer 



275° difference. 



Iron melted at a high heat 3988 by the former 

 3479 by pyrometer 



509° difference. 



A similar excess also appears in their determination of the 

 heat of melted copper, and obviously admits of the same ex- 

 planation. 



After performing these experiments upon the melting points 

 of the metals, I was desirous of ascertaining the effects of the 

 most intense heat which it was possible to produce in a fur- 

 nace; and to measure the utmost limits of expansion in a 

 platinum bar. For this purpose I made use of an excellent 

 wind-furnace in the Royal Institution, in which upon former 

 occasions hob-nails had been completely fused into a button. 



Exp. 19. — The register I, which had not been the least in- 

 jured by the previous experiments, was fitted with a new bar 

 of platinum which had been drawn as a wire, was gV^^s of an 

 inch in diameter and very ductile. The iron bar was also 

 adjusted to a new register, and both were placed upright in a 

 well luted crucible. About half an inch of powdered charcoal 

 was strewed upon the bottom to prevent any adhesion ; and two 

 soft iron nails, and a piece of unglazed Wedgwood's porcelain, 

 were thrown in for the purpose of affording some indication 

 of the degree of heat attained. The crucible was then set in 

 the furnace, another smaller crucible inverted upon it, covered 

 with coke, and the heat urged to the utmost for two hours. 

 The fire was suffered to burn out, and the crucible with its 

 contents removed for examination. It was sound, but the 

 luting had been completely fused. The nails were found melted 

 into two complete buttons, and the porcelain was partially 

 fused upon the surface. 



The register I. appeared to be uninjured, but the platinum 

 ring and wedge were loose, evidently from a contraction hav- 

 ing taken place in the substance of the black-lead. Tliis was 

 no doubt owing to the heat having exceeded that at which it 

 had been originally baked. The amount of expansion conse- 

 quently could not be measured. The platinum ring, both of 

 this and the other register, exhibited a remarkable change of 

 texture; they had become very rough and crystalline, and 

 N. S. Vol. 10. No. 59. Nov. 1831. 2 Z were 



