392 



certain deviations mid these show distinct periodicity, the general tendency 

 being toivards increasing atomic lieat mith increasing atomic iveight. 



ScHiMPF (Zeit. Pliys. Clieiii. 1910. 71, 257) has determined the 

 specific heats of many elements at various temperatures (e.g. — 150°, 

 —100°, —50° etc.). 



From Ills work he conchides that f lie atomic heats diverge in a 

 marked way as the temperature falls, whilst conversely a rise of 

 temperature produces, as is well known, a marked convergence 

 towards a fixed value for all elements. 



Evidently, it is seen from the ahove investigations, that there are 

 distinct indications showing the period nature of atomic heats at 

 low temperatures. 



Very i-ecently a decided advance in this direction was made by 

 Dewar [Proc. Roy. Soc. A. Vol. 89 p. 158 (1913)]. He determined 

 the specific heats of 53 elements between the boiling points of liquid 

 nitrogen and hydrogen at about 50' absolute. 



When the atomic heats are plotted in terms of their atomic 

 weights they reveal definitely a periodic variation resembling gener- 

 ally the well-known Ijothau iAIkykk atomic volume curve. 



The author concludes that if experiments were similarly made 

 between the boiling points of hydrogen and helium then in all proba- 

 bility the atomic heats would be all very small and nearly constant. 



However interesting these results may be there is a great difticulty 

 in these investigations. The temperature range is very high with 

 these workers. In the case of Richards of Jackson's experiments it 

 was about 200° and in (he case of Dewar's it was 57°. 5. 



From these works only the mean specific heat between so large 

 a range of temperature is availal)le and not the specific beats at a 

 fixed temperature. Since there is a marked variation of specific 

 heats with temperature, the results obtained in experiments carried 

 on with large range of temperature lose much of their significance. 



Nernst and his pupils have determined the specific heats at low 

 temperatures (Jour, de Phys. tome IX, 1910, p. 721); E. H. Grif- 

 fiths and E. Griffiths have also attacked the same problem (Phil. 

 Trans. 1913 A 213, 119.). These experiments are advantageous, 

 since the temperature range is very small. In Nernst's experiments 

 it is only 2°. 7 C. It is well known that the atomic heats of 

 elements can be calculated from Einstein's formula 



~l\r) 



C' = 3 R—^ h b ri 



C-_0' 



