Polariscopio di Duboscq

Descrizione e caratteristiche fisiche

...

Nell'oculare è inciso "Ordinaire Jaune" ed "Extraordinaire Violet".

Lo strumento è firmato "J. Duboscq à Paris".

Notizie storiche e uso dello strumento

...

Nella Nota xxx è riportato: ...

The transition-tint polariscope

Sections of quartz, cut perpendicular to the optic axis of the erystal, have a strong rotatory effect on plane polarized light when the light passes parallel to the optic axis, some crystals turning the plane of polarization to the right (clockwise), others to the left.

The transition-tint plate consists of two quartz sections, cut as described, of equal thickness, but of opposite rotations. These are mounted in a diaphragm opening between the polarizer and analyzer, in such a way that each section covers half of the optical field of the polariscope. The scctions are cut 3.75 millimeters thick, and rotate the mean yellow rays 90° (3.75 x 24 = 90), which in conscquence cannot pass through the analyzer when its plane of polarization is parallel to that of the polarizer. White, or any light containing rays of all wave lengths, as lamp or gas light, in passing through such an optical combination will be deprived of its yellow rays, and the optical field will show, accordingly, the resulting ''complementary'' tint, usually described as a rose-violet.

If the analyzer is turned, contrasting tints of red and blue are seen in opposite halves of the field. Only at the end point, or at a position of the analyzer 180° from it, do both halves of the field show the same tint, this rose-violet transition tint.

The transition-tint polariscope was introduced by Robiquet (1856), and was much used by earlier investigators, as it was more sensitive than the Mitscherlich, and had the advantage of using ordinary light.

Bibliografia & sitografia

• Biot J.B. (1840). Sur la construction des appareils destinés à observer le pouvoir rotatoire des liquides. Ann. Chim. 74, 401-430; also COMPTE RENDU 11, 413-432.

• Robiquet E. (1856). Description du diabétomètre. Appareil destiné à doser le sucre dans les urines diabétiques. J. Pharm. 29, 371-374, with instructions in 30, 277-281. Extract in Comptes Rendus Acad. Sci. Fr. 43, 920-921. The instrument is illustrated in an article by C. Bernard in Rev. Sci. 2, 970-977, 1873.

• Rolfe G. W. (1905). The polariscope in the chemical laboratory. An introduction to polarimetry and related methods. Macmillan & Co., London, pags. 16-19

• WikipediA:

• YouTube: