738 



Professor W. A. Tilden 



[May 13, 



specific heat at this lower temperature is very little less than it is 

 near the melting point. The properties of many other metals, 

 notably zinc and copper, change considerably at temperatures far 

 removed from their melting points without substantial change in 

 their capacity for heat. 



As to allotropy, it is a phenomenon which is comparatively rare 

 among metals, and in the marked cases in which it occurs we have 

 no information as to the value of the specific heats in the several 

 varieties, such as the two forms of antimony and the silver-zinc alloy 

 of Heycock and Neville, and they may be left out of account. Bunsen 

 compared the so-called allotropic tin, obtained by exposing the 

 metal to cold for a long time, and found it -054:5 against '0559 

 for the ordinary kind.* In dimorj)hous substances there is often no 

 difference. Eegnault found for arragonite • 2086 and for calcite * 2085 

 respectively. The differences between metals hammered and annealed, 

 hard and soft, were also found by Eegnault to be very small, f 



Hard steel 

 Hard bronze 



1175. Same, softened 

 0858. Same, softened 



1165 



08G2 



Kopp came to the conclusion, ^rs/, that each element in the solid 

 state, and at a sufiicient distance from its melting point, has one sj)ecific 

 or atomic heat, which varies only slightly with physical conditions ; and 

 secondly, that each element has essentially the same specific or atomic 

 heat in compounds as it has in the free state. This last is practically 

 identical with the statement which is known as Neumann's law. With 

 Kopp's conclusion I agree, but, from some of Eegnault's results 

 coupled with my own, the effect of small quantities of carbon and 

 j)erhaps of sulphur upon the specific heats of metals is greater than 

 has been supposed. If we take the results of Eegnault and of Kopp 

 and combine them with the most accurately known atomic weights, 

 the products are still not constant. 



Atomic Weights most accurately known (1897) combined 

 WITH Specific Heats. 



Copper 



Gold 



Iron 



Lead 



Mercury liq 



„ - 78° to + 10° 



Silver 



Iodine 



63-12 

 195-74 



55-60 

 205-36 

 198-49 

 198-49 

 107-11 

 125-89 



S.H. 



Eegnault. 



09515 

 03244 

 11379 

 03140 

 03332 

 03192 

 05701 

 05412 



At. Ht. 

 Kopp. 



5-87 



6-23 

 6-47 



6-00 



* Pogg. Ann. 141, 27. 



t Ann. Chim. [3], ix. 



