510 CHAPTER XXV 



Formal Instructions for obtaining the Polarization.— /z«cgs. — (a) Fill a 

 flask graduated at loo-iio c.c. to the loo c.c. mark with juice. Add suffi- 

 cient basic lead acetate to clarify and no more than necessary. Complete 

 the volume to no c.c. Shake. Filter. Reject the first runnings. Obtain 



N y. W X I'l 



the polarimeter reading. Then the polarization is =r where 



^ 100 X D 



N is the reading, D is the density of the juice referred to water at 17-5° C, 



and W is the normal weight adopted. 



(b) Transfer 52-096 grams of juice to a 100 c.c. flask referred to Mohr's 

 c.c. (or 52 grams if the flask is graduated in true c.c.) . Add lead acetate as in 

 (a), complete the volume with water to 100 c.c. Filter, etc., as in (a). The 

 polarization is one-half the observed reading. Spencer's pipette, ^^ graduated 

 with reference to degrees Brix, so as to deliver the proper quantity corres- 

 ponding to the density of the material, is used in this routine. 



(c) Place an unmeasured quantity of juice in a container. Add sufficient 



dry lead acetate to clarify. Agitate violently. Filter, etc., as in (a). Then 



. NW " 

 the polarization is ^ where N is the reading, D is the density of the juice 



referred to water at 17-5° C, and W is the normal weight adopted. This 

 method is due to Horne.^^ 



Raw Sugar. — Weigh out the normal weight. Transfer to a 100 c.c. 

 flask. Dissolve in water, making the total volume about 80 c.c. Add suffi- 

 cient basic lead acetate to clarify, but not an excess. Complete the volume 

 to 100 c.c. Shake. Filter. Reject the first runnings. Obtain the polari- 

 meter reading of the filtrate, giving the polarization of the sugar. 



The formal directions given above are substantially those adopted by the 

 U.S. Bureau of Standards,®^ and for commercial and revenue purposes 

 should be strictly followed. It is not permissible, for example, to take 

 24-32 grams and calculate the polarization. Such a variation is permissible, 

 however, to the anal3^st working as an individual, but legally the exact 

 instructions should be followed. 



In addition to the above formal instructions, the use of filtered light is 

 obligatory. For legal purposes, the observation must be made at 20° C, or 

 corrected for temperature error, as indicated in the previous chapter. 



The U.S. Bureau of Standards does not take into account the effect of 

 the volume of the precipitate, or the effect of basic lead salts on the rotation of 

 the fructose, which may be present. In a strict determination of sucrose 

 in a sugar, as opposed to a polarization, these points should be considered. 



The routine control operations also neglect these points and also any 

 temperature correction. 



Massecuites, Molasses, etc. — The routine is essentially as for Raw Sugar. 

 In actual work the following procedure is adopted by most analysts. In 

 obtaining the Brix the material is diluted i : i. Normal weight of this diluted 

 material is transferred to a 100 c.c. flask by means of a Spencer pipette and 

 clarified as for a juice. Twice the reading gives the polarization. With 

 very dark molasses it is better to use a half-normal weight of the i : i dilution. 



Alternatively, the material mav be weighed out, an integral fraction of 

 the normal weight being used, or not, at the option of the operator. 



Thirdly, a solution of any ascertained degree Brix may be made up 

 without weighing. This solution may be treated as a juice and the purity 



