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

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.

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$become, is evident from the fact, as we have already seen (§ 16, towards the end), that in some cases the alteration is so great as to cause complete reversal of the original direction of rotation, lasting only so long as the disturbing substance is present. C. Determination of the True Specific Rotation of Active Substances from the Rotatory Power of their Solutions. § 29. As we have seen (§24), the value [a], calculated from a solution of an active substance, is never the true specific rotation of the substance itself, in a state of purity. It is necessary first to ascer- tain the law of the variation brought about by the inactive liquid, by examining a number of solutions of different strengths, and then the true specific rotation may be approximately obtained by cal- culating the value of constant A in the formula [a] = A + B q, or [a] = A + Bq + C q\ &e. (see § 24). Whether this method is really reliable or not can only be prove by experiments on substances, the real specific rotation of which can be determined independently. A series of solutions of such substances of different strengths must be prepared, from the observed specific rotations of which the value of constant A must be determined, and the result compared with that obtained by direct observation Up to the present, the only investigations of this kind have been made by Biot with cane-sugar1 and tartaric acid2, the latter of which, when cast in solid plates, was found to give nearly the same specific rotation as had been deduced from its solutions by application of the formula [al = A. + -B , It was, therefore, of importance that further researches ot tae same kind should be instituted, and more particularly upon liquids since it is only such substances that admit of the specific rotation ot the absolute substance being accurately determined, as well as ot a complete examination of the changes produced by the addition ot successive quantities of various inactive solvents. In the following pages are given the results of the author s investi- gations of the rotatory powers of right-and left-handed oil of turpen- tine, nicotine, and tartrate of ethyl, taken first alone, and afterwards in 1 Biot: Mem del’Acad., 13, 39 ; Ann. Chim. Phys. [8], 10, 175. 2 Ann. Chim. Phys. [3], 28, 351. 3 Liebig's Ann. 189, 241.$