760 



Physics. — ''Further e.rperlments wWi liquid heliura M. Prelimi- 

 nary determination of the specific heat and of the thermal 

 conductivity of mercury at temperatures obtainable loith liquid 

 helium, besides some measurements of thermoelectric forces 

 and resistances for the purpose of these investigations '. By 

 H. Kamerlingh Onnes and G. Holst. Communication N°. 142c 

 from the Physical Laboratory at Leiden. 



(Communicated in the meeting of June 27, 1914). 



§ 1. Introduction. Measurements of the specitic heat and of the 

 thermal conductivity of mercury were considered to be of special 

 importance with a view to the discontinuity, found at 4°. J 9 K. in 

 the galvanic resistance of this metal. The preliminary results have been 

 already mentioned in Comm. ]S°. 133, for the measurements were 

 carried out as early as June 1912. We wished to repeat the experi- 

 ments, which we considered only as a first reconnoitring- in this 

 region, because our opinion was, that, by some improvements in the 

 experiments, the accuracy of the results could be considerably 

 increased. Special circumstances frustrated this, aud now, as there 

 seems to be no prospect of a repetition for the present, we com- 

 municate the details of our investigation. 



§ 2. Thermoelectric forces. The tirst difficulty in these deter- 

 minations was the choice of a suitable thermometer. The measure- 

 ments already performed about the resistance of platinum, gold and 

 mercury did not give much hope, that there would be among the 

 metals a suitable material for resistance thermometers. We have 

 therefore investigated a series of thermoelements. The gold-silver 

 couple, a suitable thermometer at hydrogen temperatures ^), showed 

 down to the higher heliura temperatures a fairly large thermoelectric 

 power, at the lower helium temperatures, however, the thermoelectric 

 power diminishes rapidly, so that this couple did not satisfy the 

 requirements. Moreover, this couple was not at all free from disturbing 

 electromotive forces, which appeared at places of great fall of tem- 

 perature in the cryostat, Nearly all other elements were subject to the 

 same fault. But apart from this, none of the combinations was suitable. 

 Notwithstanding, we communicate the results of our determinations, 

 because they show clearly that according to the theoretical investi- 

 gations of Nernst and Keesom ^), the thermoelectric power of all 



^) Compare H. Kamerlingh Onnes and J. Clay, Comm. N". 107Ö. 

 2) W. Nernst, Theoi-. Chem. 7e Aufl. 1913 p. 753. Berl. Sitz. Ber. 11 Dez. 

 1913 p. 972. 

 W. H. Keesom, Leiden. Comm. Suppl. N^. dOb (Proceedings May 1913). 



