Page:Outlines of Physical Chemistry - 1899.djvu/92

 ��OUTLINES OF PHYSICAL CHEMISTRY

��of the theory of a typical apparatus may be given, and for this purpose we shall select Pulfrich's Be) 'Tactometer. }

This apparatus is comparatively simple, and Bruhl's improved form, furnished with a thermostat, is applicable over a long range of temperature.

Fig. 11 gives an idea of the arrangement.

���The liquid or fused substance is placed in a small glass vessel which is fixed above a glass prism. The refractive index of this prism, which must be a right-angled one, must be known (it is generally 1*61). .

A beam of light ia allowed to enter the prism very close to and in the direction parallel to the horizontal surface of separation of the liquid and the glass (the angle of incidence, i u is then 90°), and leaves the prism making

1 Fig. 12 shown Pulfrich's Befractometer.

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