Abstract
The quantitative determination of organic compounds by means of their optical activity is often convenient, and it is often necessary to employ small amounts of the solutions to be investigated.
Emil Fischer's micro-polarimeter 1 has been used but very little, and it became impossible to follow his technique because of the inability to obtain the Nernst light as a consequence of the war, but I have applied the principle with several modifications, while using the Schmidt & Haensch polariscope, which permits of readings of 0.01 degree, and specially prepared capillary tubes which are 50 millimeters, and 100 millimeters in length, respectively, and which have an inside diameter of about 1.5 millimeters. The walls of the tubes are 3 mm. in thickness.
It is especially necessary that the tubes be perfectly straight. They hold 0.1 c.c. and 0.2 c.c. respectively, of the solution to be tested, the specific gravity of which is determined by means of a pycnometer holding 0.2 c.c.
The following method was used for the source of light: To a solution of 1.25 Gm. of pure uranium sulyhate in 50 c.c. of distilled water was added 0.5 Grn. zinc powder and 1.8 c.c. of sulphuric acid, in three portions. After four hours, when the reaction was complete with the conversion of the uranyl sulphate into the uranosulphate, 2 cm. in length, the solution was filtered and the anterior cell of the polarimeter was filled with this solution completely avoiding air bubbles. The posterior cell, 2 cm. in length, was filled with a six per cent. solution of potassium bichromate. An electric lamp of opalescent glass of 150 watts intensity was placed in a galvanized iron casing into the side of which was fitted a telescope tube, permitting of variation in the distance of the light, and into which the end of the polariscope projected.
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