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\ 
Physics. — “On Nernst’s theorein of heat.” By Prof. Pa. KounsitamM 
and Dr. L. S. ORNsreiN. (Communicated by Prof. J. D. vAn. 
DER WAALS.) 
1. Recently Dr. F. EB. C. ScHeFrer drew attention in an address*) 
to Neryst’s ‘theorem of heat”. This “theorem of heat” consists in 
the “supposition” that at the absolute zero the quantities A and 1 
Le. the maximum work and the change of energy for a chemical 
reaction in a condensed system would not only be equal, but would 
also have the same differential ‘quotient with respect to temperature. 
It is not said explicitly that in the differentiation the volume is sup- 
posed constant, but it may be assumed that this is meant. This 
theorem of heat enables us, to express the constant of integration of 
vAN ’T Horr’s equation: 
din K J 
at ee 
in the constant of integration of CLAPEYRON’s equation applied to the 
saturate vapour: 
in which for 2 is chosen an empirical expansion into a series. In 
this way Nernst finds that the constant of integration of vaN ’T Horr’s 
equation, C, (when the A’ is expressed in partial pressures), is in 
connection with the constant of integration of the vapour pressure, 
c, according to the equation: 
OC SS 0er Sh) wa Veg) Gey ee ee 
in which vy is the number of molecular quantities of every substance, 
which take part in the reaction, and the + sign is to be extended 
over all the substances, the disappearing substances being counted 
negative. 
By the aid of suppesitions about the specific heats which we 
need not discuss here, and of the experimental data of the vapour 
pressure lines Nernst determines the value of c for a number of 
substances from the formula for their vapour pressure line found by 
the empirical expansion into series for 2. It now appears that for 
some of these substances this c has about the same value, namely 
about 1.1 f, in which f is the factor from vaN DER Waats’ well- 
known empirical vapour pressure formula. This enables him to find 
a value of ec also for substances whose vapour pressure line is not 
1) See Chemisch Weekblad 1910, NO, 43. 
