1014 
it; these values are entirely independent of the entropy of the solid 
substance. The gas entropy is namely found then by examining the 
probability of the gas state; if this is done at temperatures where 
solid substance is impossible, so far above the melting-point, the 
chance to a solid configuration must be entirely excluded. When the 
iodine equilibrium is tested, where the temperatures amount to 
1000° K. and more, the chance to solid substance (melting point 
387° K.) may certainly be put zero. And therefore the expressions of 
Sackur, TeTRODE, and vaN DER Waars will in my opinion yield the 
correct values for the moment of inertia, and the test remains entirely 
outside the theorem of heat, in whatever form it be. 
If, however, for the entropy of gas i log W has been chosen — 
I will call these values the gas scale for the entropy — it is the 
question what will be the entropy of solid. This value might 
d 
either be determined by means of Sa or by applying the 
expression k log W also to the solid state. The latter, however, is 
only feasible on the assumption of one or more hypotheses concern- 
ing the constitution of the solid substance; these derivations must, 
therefore, certainly remain arbitrary in a high degree. For a mon- 
atomic solid substance a comparatively simple mechanism may be 
devised corresponding to the properties of solid *), but for multi-atomie 
solid substances the model becomes necessarily more intricate, hence 
more arbitrary. ”) 
If it is, however, assumed, as is often done, that the entropy of 
solid at 7’=0 is zero, then starting from this the entropy of other 
eee Oh 
states can be determined with the aid of dS=—, - This scale of 
entropy, which I will eall the scale for solid, need not coincide, 
however, with the gas scale in my opinion. And if it does so for 
one substance, this need not necessarily be the case for all. At any 
rate this coinciding of the two scaies requires experimental verification. 
The only data from the literature which can furnish such a test, 
are in my opinion: 
1. the theoretical derivations of SrerN's gas entropy. 
2. the vapour pressure line of mercury. 
! gas dQ En 
3. the calculation of > — for iodine. 
solid T=0 
1) Stern, Physik. Zeitschr. 14 629 (1913). 
*) Srern, Ann. der Physik. (4) 44 520 (1914). 
