Jg4 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1936 



of Leiden. Extensive abstracts are published in Rapports des Con- 

 gres Internationaux du Froid. 



ADDENDUM BY PROFESSOR KEESOM 



Since its establishment the excellence of the installation of the 

 Kamerlingh Onnes Laboratory has attracted many foreign investi- 

 gators. Numerous American scientists have even crossed the Atlantic 

 to work there. The following is a summary of their principal 

 investigations : 



A. L. Clark, in collaboration with Kuenen, studied the critical 

 jjroperties of the air. Gray employed a baroscope serving to deter- 

 mine easily, rapidly, and with great precision the densities of gases 

 and vapors. 



G. Breit measured the magnetic susceptibility of chromic chloride 

 and of gadolinium sulphate in an alternating field at the boiling 

 temperature of hydrogen. He was unable to find any evidence of 

 hysteresis in the magnetization of paramagnetic crystals. He also 

 measured the dielectric constants of liquid hydrogen and oxygen. 



In collaboration with Kamerlingh Onnes, Dana measured the latent 

 heat of vaporization of helium and found a point of inflection at 

 2.° 19 K., which is the point of transition from Hci to Hen. His 

 measures on the specific heat of liquid helium were unable to yield 

 the point of the cusp because the experimental technique had not 

 then been sufficiently developed. 



Donald H. Andrews measured the specific heat of certain organic 

 molecules and of lead. 



Very recently Dr. Chester W. Clark has made important measure- 

 ments on specific heats. For gadolinium sulphate he extended the 

 measurements and confirmed the anomalous behavior of the specific 

 heat at about 3.° 8 K. For potassium chloride he found that the 



values of d of Delbije (defined by the equation ^5=4661 q ) > C^ being 

 the specific heat at constant volume) do not tend toward zero, as 

 in the metals (silver, for example) but only diminish. This proves 

 that the anomalous variation of 6 for the metals is caused by a 

 specific heat proper to the free electrons. For, by subtracting this 

 heat from the heat observed for the metals, the values of 6 thus 

 obtained give a curve identical with that of potassium chloride. 

 Dr. Clark has also measured the specific heat of nickel, which is 

 ferromagnetic. Debije's formula is not followed, and the variations 

 from it do not follow exactly the formula of Sommerfeld for the 

 contribution of the free electrons. These results have inspired Pro- 

 fessor Mott to theoretical considerations of much interest. 



