MlCRO-POLARIMETER 



203 



Emil Fischer's micro-polarimeter 1 has been used but very lit- 

 tle, 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 sulphate in 50 c.c. of dis- 

 tilled water was added 0.5 Gm. zinc powder and 1.8 c.c. of sul- 

 phuric acid, in three portions. After four hours, when the re- 

 action was complete with the conversion of the uranyl sulphate 

 into the uranosuiphate, 2 cm. in length, the solution was filtered 

 and the anterior cell of the polar imeter was filled with this solu- 

 tion 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. This arrangement avoids the disturbance due to 

 external light. 



The capillary tubes were not encased in hard rubber, since that 

 interferes with the observation of air bubbles during filling, 

 but after filling they were placed in a previously slit -rubber tub- 

 ing. It was then found that the light which penetrated the glass 

 walls of the tubes introduced a disturbing factor and this was 

 avoided by covering the ends of the capillary tube with black 

 paper which had an opening corresponding to the inside diameter 

 of the tube. This arrangement insured that only that light which 

 passed through the solution in the capillary tube passed on to the 

 eye piece of the polarimeter. 



i Ber. a. deut. chem. Gesell, 1911, xliv, 129. 



