A system of physical chemistry - Index of

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A system of physical chemistry - Index of

ATOMIC HEATS OF SOLIDS 57

ing to the vibration frequency of atoms are naturally far in the infra-red

region. The is apparatus employed shown diagram matically in the

figure (Fig. 7). L is the electrically heated black body emitting waves

of all frequencies. D^ and Do are diaphragms of small aperture. S is

a screen. The diaphragms and screen are kept cool with water at room

temperature. The substance under examination is represented by

Pi, P2, P3, P4. The surfaces of these pieces are polished as highly as

possible. M is an adjustable mirror and T the thermopile. A diffraction

grating of special make could be inserted in the path of the beam,

thereby analysing it into a spectrum, the position of the energy maxima

of the substance

corresponding to the characteristic vibration frequencies

P being determined by means of the thermopile. In later experiments

the grating had to be abandoned owing to the large amount of absorp-

FiG. 7.

tion suffered by the rays in it. passing through Instead, an interference

method has been devised— see the paper by Rubens and HoUnagel,

Fhil. Mag., i.e. The following table contains some of the results

summarised by Rubens and von Wartenberg {Sitzungsber. kbnigl. preuss.

Akad., 1 91 4, p. 169). In actual experiment two bands are usually observed

fairly close together. One of these, however, is due to the

presence of water vapour (Rubens, ibid., 1913, p. 513)-

Residual Rays Characteristic of Certain Solid Salts.

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