1893.] MICROSCOPICAL JOURNAL. 233 



MICROSCOPICAL APPARATUS. 



Proposed Adaptation of Biot's Apparatus to the Micro- 

 scope. — A. Cani})bell Stra'k in a note read at a meeting of the 

 London Chemists Assistants' Association stated that some time 

 ago in order to illustrate the fact that a column of certain kinds 

 of liquids alter the direction of a ray of polarized light, he 

 placed a trough containing turpentine on the stage of a micro- 

 scope, and by means of the prisms used in polarizing, he was 

 able to demonstrate that fact. This suggested to him that the 

 analyzer and polarizer of the microscope might be used in an 

 adaptation of Biot's apparatus for measuring the circular polar- 

 ization of liquids. 



The proposed apparatus should consists usually of a tube 

 of glass, covered with tin-foil, about 20 centimeters long and 

 closed at each end with parallel glass plates, which can be 

 screwed on and off. This tube fits into that of the microscope, 

 between the stage and eye-piece. The polarizer is placed below 

 the stage, and the analyzer in the position of the eye-piece. 

 Over the analyzer is placed a cap bearing a piece of red glass, 

 so that the emerging light is rendered monochromatic. The 

 microscope is now placed horizontally, and the reflecting mirror 

 moved aside. The flame of a lamp is brought within a few 

 inches of the lower end of the polarizer. The lamp-glass should 

 bear a black spot, which gives the extraordinary image at the 

 other end of the system. 



When these have been arranged, the tube of the instrument is 

 moved as close to the polarizer as possible, and one of the prisms 

 is turned so that the extraordinary image disappears, and very 

 little light passes. On filling the tube with an optically active 

 liquid, the extraordinary image and the light reappear, and the 

 prisms must be turned right or left so as to cause the image to 

 vanish. The arrangement carrying the analyzer should be pro- 

 vided with a fixed scale, divided into degrees and furnished 

 with an indicator. 



Ordinarily, the whole cost of adapting this contrivance to a 

 good microscope is but a few shillings, and it furnishes means 

 of ascertaining, (1) Whether a liquid is optically active, (2) 

 Whether dextro or Isevo- rotatory, (3) The relative optical activ- 

 ity of several liquids. — Druggists, Circular 6c Chemical Gazette, 



