THE POLARISCOPE AS APPLIED TO SUGAR ANALYSIS. 



Wild Polariscope. 9 This pattern, which is seldom met with, obtains 

 its end point by means of the interposition of a Savart polariscope between 

 the polarizer and analyser, the former being rotated in making a reading. 

 When adjustment is nearly obtained a number of horizontal dark bands occupy 

 the field of vision ; on further rotation of the polarizer those occuping the 

 centre of the field disappear, leaving a clear, bright, vertical band, defined by 

 a circular banded part on either side ; in the field of vision are arranged cross 

 hairs, the end point being taken when the three parts of the field are 

 symmetrically arranged about these. 



Trannin Polariscope. In this instrument the analyser and 

 polarizer are fixed, and adjustment is made by varying the length of the 

 polariscope and concentration of the solution. 



Broch Polariscope. This instrument combines the spectroscope 

 with the polariscope and obtains its end point by the coincidence of a dark 

 band in the field of vision with the Praunhofer D line. These last two 

 instruments find no use in sugar analysis. 



The Saccharimeter as distinct from the Polariscope. 



In the above descriptions of devices used in polariscopes it was stated that the 

 angular rotation was measured by rotating the analyser in an opposite direction 

 to that due to the active material, the rotation being measured directly in 

 angular degrees, and that monochromatic spectrally purified light was used. 

 In polariscopes made specially for sugar analysis ordinary white light is used, 

 the rotation is measured on a linear scale graduated up to 100, the 100 point 

 corresponding to the rotation produced by normal weight of pure sugar dis- 

 solved in 100 cc., and observed in a tube 20 cm. long; the rotation produced 

 by the sugar solution is neutralized by the interposition of a plate of active 

 quartz, the thickness of which can be varied, and which is proportional to the 

 scale reading, the device being known as a compensator. 



Normal Weight. By this term is meant that weight of pure cane 

 sugar which, dissolved in 100 cc. of water, and observed in a tube of length 

 20 cm., gives a reading of 100 on the scale of the polariscope. 



There are several normal weights in use. Ventzke, the optician, whose 

 name is connected with the transition tint polariscope, adopted as a standard 

 sugar solution, one of density 1-1, at a temperature of 17'5C. ; such a solution 

 contains 26-048 grms. of sugar in 100 Mohr's c.c., and this weight of sugar 

 became a very generally accepted normal weight. Mohr's c.c., i.e., the volume 

 occupied by a grm. of water at 17'5C., is deservedly falling into desuetude, 

 and since 26-015 grms. per 100 true c.c. are equivalent to 26-048 grms. per 

 100 Mohr's c.c., a normal weight of 26 grins, per 100 true c.c. has been 

 strongly recommended for adoption. 



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