234 PROFESSOR W. A. TILDEN ON THE SPECIFIC HEATS OF METALS, 



Both metals are now obtainable in a pure state, and after melting and solidification 

 under the same conditions are presumably in the same state of aggregation. Their 

 atomic weights, though not known exactly, are undoubtedly very near together, as 

 are also the densities of the metals and other of their physical properties. 



The specific heats of cobalt and nickel were estimated by REGNAULT, using the 

 method of mixtures, with the following mean results : 



Nickel, -1090. Cobalt, -1067. 



The metal in both cases, contained carbon, and the cobalt probably contained 

 nickel. 



In the choice of the method for estimating the specific heat, my attention was 

 drawn to the excellent results obtained by Professor J. JOLY in the use of his 

 differential steam calorimeter. 



It is unnecessary for me to describe the apparatus I have used, for it has been very 

 carefully described by its inventor,! to whom I am greatly indebted for instructing 

 the makers of the instrument in my possession. In using the instrument, all I have 

 done by way of modification is to add a condenser for the escaping steam, and to take 

 great precautions in determining the temperature of the space within the inner 

 cylinder of the calorimeter by jacketing the thermometer and reading with a 

 telescope ; also in protecting the substance in the carrier from drip. The weights 

 were all reduced to their equivalent in vacuo, due allowance being made for the 

 exchange of the atmosphere of air for one of steam at 100. 



The following formulae were used in the calculations : 



where S is the specific heat, W the weight of the metal in vacuo, w the number of 

 grams (or cubic centimetres) in vacuo of water condensed by the metal, t l the 

 temperature of the calorimeter full of air before the admission of steam, t 2 the 

 temperature of the steam in the calorimeter, and X the latent heat of steam at 

 barometric pressure ; and 



w = wj_ + w8 - (VjD - V 2 8) 



' ' 



in which w { is the apparent weight in steam of water condensed by the substance, 

 Vj is the volume of the substance at <i, V 2 is the volume of the substance at t 2 , D is 

 the density of the air at < 1 and barometric pressure corrected to 0, 8 is the density 

 of the steam at t z and barometric pressure. A small correction ('0003 gram) had to 

 be applied to one carrier to make it calorimetrically equal to the other. 



* ' Ann. Chim. Phys.' [3], vol. 63, p. 23. 

 t ' Roy. Soc. Proc.,' vol. 47, p. 241. 



