Tests and applications of the third law

It was shown experimentally by Simon and Swensenf that dp/dT is extremely small or zero below 1.4 K. The differential coefficient was actually found to be proportional to the seventh power of T, 

According to the third law SS tends to zero and therefore so also must (d8jdp)x Using one of the Maxwell relations it follows that dVjdT)p must also tend to zero as This has been confirmed experimentally in the case of copper, aluminium, silver and other substances. 

Finally, let 8a — be the entropy increase in the process the equilibrium temperature as calculated from the latent heat, and let 8a — denote the extrapolated entropy difference as 

Since entropy is a function of state its change round a cycle is zero. 

Despite the good agreement in the table above it must be admitted that any application of the third law to metastable states is somewhat precarious, and is perhaps justified only in cases where we seem to have a fairly clear statistical insight. 

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