76^ 



tb in laj'er of pentane, which is 

 spread over the glass, acts as a 

 viscous lubricant at this temperature 

 and prevents the sticking of the 

 mercury to the wall in freezing. 

 After haviug been frozen, the little 

 block of solid mercury was screwed 

 up by means of the handle K 

 and the temperature was increased 

 to about — 50° C. Thereupon a 

 high vacuum was established by 

 means of a Gakde mercury pump 

 and the pentane was distilled off 

 into a tube, immersed in liquid air. 

 During the experiments the heat 

 insulation of the block appeared 

 to be so good, that the tem- 

 perature remained many degrees 

 above that of liquid helium, al- 

 though it was let down against 

 the glass wall. Therefore a little 

 gas had to be admitted in order 

 to cool the block. This manipula- 

 tion succeeded perfex?tly, but the 

 gas could not be removed quicltly 

 enough in the short time available 

 for the experiments. The loss of 

 heat of the mercury was thus 

 very considerable (decrease of the 

 temperature difference to half of 

 the original value in about J 00 

 seconds) and therefore the cor- 

 rection, to be applied to the in- 

 crease of temperature while heat- 

 ing, remains the greatest soui'ce of 

 Fig. 2. Fig. 3. uncertainty. Nevertlieless it seems 



possible, that the results are accurate to about 10 7^. 



The thermal capacity of the hollow steel cylinder with the thermo- 

 meter and the heating wires was determined afterwards by a separate 

 experiment, Fig. 3 shows the apparatus used for this purpose. 



h. Results. Measurement at the boiling point of IteUuin. The quantity 

 of heat supplied to the mercury amounted to 1,10 cal., the increase of 



