Handbook of the polariscope and its pracitcal applications / adapted from the German editon of H. Landolt, by D.C. Robb and V.H. Veley.

  • Hans Heinrich Landolt
Date:
1882
Catalogue details

Licence: Public Domain Mark

Credit: Handbook of the polariscope and its pracitcal applications / adapted from the German editon of H. Landolt, by D.C. Robb and V.H. Veley. Source: Wellcome Collection.

    66/320 (page 46)
    to mean yellow light—the wave-length of which may be taken at about 0-00055 millimetre. The angle of rotation and the specific rotation thus obtained are indicated by a, and [a], (jaune moyen) respectively, as proposed by Biot. ,, , Now the wave-length of this mean yellow light is less than that of the ray D, which lies on the border between orange and yellow, so that the value of a, is always less than that of «Dh For example, with quartz, according to Broch, aD = 21'67°, and a, — 24 , so t la , to express the one in terms of the other, we have 24-5 at = aD = 21*67 21-67 24-5 aD= lT306aD, or approximately = 9/s aD i a, = 0-8845aj, or approximately = 8/9 ay The proportion, however, between aj and aD vanes in different substances, according to their different rotatory dispersions. J. de Montgolfier2 has determined it in the following Quartz (according to Broch) aD : a, = 1 : 1 131 Aqueous solutions of Sugar „ „ 1:1 129 Alcoholic solutions of Camphor „ „ 1 : 1-198 Oil of Turpentine „ »» 1 : 1’2!3 According to L. Weiss,8 in aqueous solutions of sugar contain- ing 5 to 19 grammes in 100 cubic centimetres, the proportion is aD: a, = 1 : 1’034. , In any other substance, the rotation for one ray can be estimated from that for the other only approximately, by assuming that the rotatory dispersion of the substance agrees with that of some one of the preceding. As the transition tint corresponds to no sharply-defined ray, its use is attended with inconvenience, and latterly has been mostly abandoned. Many older observations are in existence, made by Biot with red light, obtained by transmission through glass coloured by suboxide of copper, with a refrangibility about equal to that of Fraunhofer’s line C. Assuming that, on passing through a quartz plate 1 milli- metre thick, it experienced rotation through an angle of 18 414 , Wild4 calculates its wave-length to be 0*000635 millimetre. The ratio between this red ray and the transition tint Biot5 gives as 23 : 30. 1 By many observers the values of a} and aD have been taken as equal, a confusion which has been remarked upon by J. Montgolfier, Bull. Soc. Chim. 22, 487, and Biban, idem, 22, 492. 2 Montgolfier: Bull. Soc. Chim. 22, 489. 3 Weiss: Sitzungsber. der Wiener Acad. 69, 157, IHte Abth. 4 Wild : Polaristrobometer, p. 35. 5 Biot: Mem. de V Acad. 3, 177.