. Practical physical chemistry . The Lippich polarimeter differs from the Laurent form onlyin the method of producing the half-shadow. Instead of thequartz plate, there is a small Nicol prism which covers half ofthe opening at the end of the polarizer tube. The eflfect pro-duced is the same as with the quartz plate, and the apparatuspossesses the. advantage that it can be used with light of anywave-length. The complete polarimeter is shown in Fig. 37. At the end S, which is directed towards the source of light,are the lens and the light-filter, consisting either of a solutionof potassium bichr
. Practical physical chemistry . The Lippich polarimeter differs from the Laurent form onlyin the method of producing the half-shadow. Instead of thequartz plate, there is a small Nicol prism which covers half ofthe opening at the end of the polarizer tube. The eflfect pro-duced is the same as with the quartz plate, and the apparatuspossesses the. advantage that it can be used with light of anywave-length. The complete polarimeter is shown in Fig. 37. At the end S, which is directed towards the source of light,are the lens and the light-filter, consisting either of a solutionof potassium bichromate or of a crystal of this salt. Thepolarizing prism is at P, and is connected with the lever h, by ii6 PRACTICAL PHYSICAL CHEMISTRY means of which it can be rotated, and thus the angle of halfshadow altered. The observation tube is placed in the middlepart of the instrument, and is protected from extraneous lightby a hinged cover. The analyzer is placed in the portion ofthe lube at A, and can be rotated, independently of the. Fig. 37. graduated circle, by means of a screw. This allows of thecorrection of the zero point. F is the telescope with is a graduated disc, which can be caused to rotate, alongwith the analyzer and telescope, past the fixed verniers « andn by means .of the rack and pinion T.* By means of the two Various arrangements are employed for rotating the analyzer, and thebetter instrumentfare also fitted with a fine adjustment. OPTICAL MEASUREMENTS 117 movable magnifying lenses /, the accuracy of the reading isincreased. Source of Illumination.—hs has already been said, theangle of rotation depends on the wave-length of the light is therefore necessary to employ monochromatic light. Onaccount of the ease with which the yellow light of the sodiumflame (corresponding with the D line of the solar spectrum)can be obtained, most polarimetric measurements are carriedout with this light. For methods of producing the sodiumflame, see p. 99. In
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