592 



Professor Sir James Dewar 



[March 25, 



about 60° C, and for graphite about 0°C. But for this discovery, 

 the trend of the curve, as shown in the diagram, Fig. 5, would have 

 pointed to the vanishing of the specific heat of carbon about —90° C, 

 a result which could not be accepted as final. The investigations 

 carried out recently,* have cleared up this point, and verified the 

 existence of the points of inflection. The following table sum- 

 marises my observations on the specific heats of diamond, graphite, 

 and ice : — 



* This is from - 18° to - 78° in the ice experiment. 



These results for diamond and graphite accord well with those of 

 Professor Weber over common ground. He gives 0*0806 for the 

 diamond between 21J° and —80°, and O'lSOl for graphite over the 

 same range. 



The second curve in the diagram, Fig. 6, shows the sequence be- 

 tween Professor Weber's results and my continuation to low tempera- 

 tures, and demonstrates the reversal of the curvature of the curve at 

 low temperatures. Similar results were got for carbon. 



The results for ice follow much the same order of change. A 

 reference to the table above shows that the mean specific heat of ice 

 falls from 0-463 at -46°, to 0-285 at -l::5;5°, and0'146at -220°C.; 

 that is, in the lowest range of temperature between the boiling points 

 of oxygen and hydrogen, it is only one-third of its value between 

 — 18° and the temperature of boiling carbonic acid. 



It would be a matter of interest to investigate the general 

 behaviour of various groups of substances, as regards their specific 

 heats at low temperatures. Without having attempted any ciireful 

 systematic investigation, the following observations extracted from 

 laboratory records are fairly representative of some classes of 

 bodies. In the table the specific heats of two alloys are given, 

 which were used in the course of the investigation ; also those of 

 sulphur, selenium, and tellurium. Two alums, on which Kopp had 

 made some observations, Avere included in the research, together 

 with tliree other typical salts. Again, naphthaline and paraffin were 

 a pail', whose specific heats were examined ; also the chloride, 

 bromide, and iodide of silver. The results for the solidified gases, 

 carbonic acid, ammonia, sulphurous acid, were of obvious interest,. 



* Proc. Kov. See, 1905. 



