252 



PROFESSOR \V. A. TII.DEN ON THE SPECIFIC HEATS OF METALS, 



sion of pure nickel and cobalt with temperature. We have taken his observed 

 numbers, and found what may roughly be taken to be the ti"ue coefficient of cobalt. 

 As he had only two changes of temperature, we are compelled to assume that a is a 

 linear function of the temperature, and we find 



a = (2-598 + -003775*) 10~ s 



We can therefore say that the heat (in gramme-centigrade degrees) given to 

 1 gramme of cobalt during an increase of temperature dt, and an increase of pressure 

 dp, is, taking JOULE'S equivalent as 4 '2 X 10 7 ergs, 



= K.dt -(6-186 - 



If instead of change of state being expressed in terms of dt and dp, it is expressed 

 in terms of dt and dv, we can only use this result if we can calculate dp. This 

 needs a knowledge of e, which we do not possess for either cobalt or nickel, even at 

 one temperature. It is, however, worth while making the following rough approxi- 

 mation. 



In pounds per square inch e is, for iron, 2*1 X 10 7 (KELVIN'S article on Elasticity) ; 

 for copper, 17 X 10 7 (BUCHANAN) ; and 2 -4 X 10 7 (KELVIN'S Elasticity). 



We cannot do better in making a first approximation than to take e for solid 

 cobalt as 2 X 10 7 Ibs. per square inch, or in C.G.S. units 



e = 1'38 X 10 12 degrees per sq. centim. 



under all conditions. 



We shall not be far wrong in assuming that, within Dr. TILDEN'S range of tempera- 

 ture, the above value may be taken for a. 



We have taken v at 21 C. as 1 -r 87181, or 0'1148 cub. centim. 



In each case, therefore, it is easy to find K k, or a 3 . e. vt, which must be divided 

 by JOULE'S equivalent 4 -2 X 10 7 , to convert the specific heats from ergs to heat 

 units. The last column shows that the two specific heats are nearly equal. 



It is interesting to note, not merely in cobalt and nickel but in any metal, that if 

 we take K to be either the specific heat at constant volume or pressure, the ratio of 

 K to k is very large at ordinary temperatures. Thus taking values from the tables 

 prepared by Professor GRAY for the Smithsonian Institute : 



