A system of physical chemistry - Index of

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A system of physical chemistry - Index of

^3o'7t

T

(^^oWt _ ij2

ATOMIC HEATS OF SOLIDS 53

- approximates to unity, so that the atomic heat becomes

equal to 3R. Dulong and Petit's Law is, therefore, a consequence of

Einstein's theory when the temperature is not too low. This region of

temperature is evidently reached at room temperature in the case of

the majority of metallic elements. As in radiation phenomena we see

that the equipartition principle applied in the ordinary way yields results

(in connection with atomic heat) which are in agreement with experiment

when the temperature reaches a certain magnitude. Einstein

tested his equation not on the data available in the case of a metal but

on the diamond. Some of the results are given in the subjoined table.

They are also indicated by circles in the figure, Einstein chose the

experimentally determined value for Cd at T = 331*3° and hence

calculated v, using the value so obtained to calculate the values of Qy at

other temperatures. The experimental data (quoted) refer, as a matter

of fact, to i.e. the atomic heat at constant Q.p, pressure. In the case of

the diamond—

though not so in other cases— the difference between

C^ and Cd is small. In the following section we shall consider the

question of the independent determination of v and Ci, respectively.

Atomic Heat of

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