Immagini

DESCRIPTION

From the relation α = kcl where k is the rotative power, c the concentration of the solution and l the thickness of the solution traversed by the light, the polarimeter is used if the rotative power is known to determine the concentration of the solution. The substance commonly used is sugar: and the polarimeter is also called a saccarometer.

To obtain a greater sensitivity, the polarimeter has a half wave plate for the monochromatic light covering half the visible field. This light illuminates a Nicol prism; the extraordinary beam exits linearly polarized and half enters the liquid sample; the other half passes also the half wave plate. The two rays, both linearly polarized but with different polarization angles, are then analyzed by the second nicol. The eye sees two fields illuminated differently. Upon rotating the analyzer by 360° one see the illumination changes in the two fields. One can determine two positions in which both are equally strongly illuminated and two in which both are equally weakly illluminated. The latter angle is to be used to maximize the sensitivity on the measurement.

This measurement is made with and without the solution. The difference between the two positions is the angle that the optically active substance has rotated the polarization plane of the light.

Our polarimeter is supported by a brass column fixed to one end of a rectangular wood base. At the other end there is a lamp holder for two gas lamps, used as the source of monochromatic light (photo-5). The double vernier which permits angular precision of 0,2' is notable.

ISCRIZIONI

1. Incisioni sul disco: Polarimetre Laurent. Incisioni sulla manopola circolare: Laurent succr. De Soleil rue de l'Odéon, Paris.

Dati Catalografici