THE CUBA R E \' I E W 



WHY CANE SUGARS ARE POLARIZED 



Whj' cane sugars are polarized and what ingredients are sought after in the examina- 

 tion by the polariscope is an important question fully answered by Dr. C. A. Browne, Ph. D., 

 chemist in charge of the Xew York Sugar Trade Laboratory and an authority upon 

 methods of polarizing sugars, in a recent issue of the American Sugar Industry of 

 Chicago. Dr. Browne says that cane sugars are ordinarily polarized in order to arrive 

 at a basis of valuation. The polarization of a sugar is reported in the degrees of a scale, 

 the 100-degree point of which represents the reading obtained upon a saccharimeter by 

 a standard weight of chemically pure sucrose under certain prescribed conditions of 

 temperature, volume, length and light. The German sugar scale is the one most gen- 

 erally employed in the United States ; a sugar degree of this scale, according to the 

 U. S. Bureau of Standards' certificates of standardization, is defined as follows : "A 

 sugar degree is one-hundredth part of the rotation shown by 26 grams of sucrose dis- 

 solved in water and the volume made up to 100 metric cubic centimeters, for light from 

 an incandescent gas mantel passed through 1.5 centimeters of a 6 per cent potassium 

 bichromate solution, the temperature being 20 degrees C. for graduation, preparation 

 and observation." This definition holds only for a 200mm. tube. 



The polarization of a sugar gives the actual percentage of sucrose only with sub- 

 stances which contain no other optically active ingredient that would affect the reading 

 of the saccharimeter and where no contaminating impurities occur which would increase 

 or diminish the polarizing power of the sucrose. The polarization for example of a 

 refined sugar damaged by water would give the true percentage of sucrose. On the 

 other hand, the polarization of a raw beet sugar containing raffinose would give more 

 than the true percentage of sucrose for the reason that the impurity raffinose has a 

 polarizing power of the same character as sucrose and of a much greater degree : so 

 also the polarization of a raw^ cane sugar would give less than the true percentage of 

 sucrose for the reason that the impurity invert sugar has a polarizing power of a 

 character opposite to that of sucrose, thus diminishing the reading of the latter upon 

 the saccharimeter scale : so again the polarization of a sugar contaminated by salt would 

 give less than the true percentage of sucrose, for while salt itself has no polarizing 

 power, its presence exerts a depressing influence upon the polarizing power of sucrose. 



These statements pertain only to the so-called direct polarization of a sugar, by which 

 is meant the reading of a solution of a sugar upon a saccharimeter without other treat- 

 ment than that of clarification.' By means of the Clerget, or invert polarization, in 

 which the reading of a standard weight of a sugar is taken before and after inversion 

 ("with acid or invertase), it is possible to arrive at a very close approximation to the 

 true percentage of sucrose. The inversion method, however, on account of its com- 

 plicated character is not employed commercially in the valuation of raw sugar, although 

 it is frequently used in factor}^ control work, where it is necessary to determine the 

 losses of sugar at the different stages of manufacture. 



The difference between polarization and true sucrose content of raw cane sugars may 

 be seen from the following table. 



Kind of Sugar Polarization Acutal Sucrose Difference 



Java Centrifugal 98.5.) 98,75 0.20 



Peru Centrifugal 97.45 97.60 0.15 



Cuba Centrifugal 04.50 95.10 O.GO 



Louisiana Centrifugal 93.70 94.50 O.so 



Louisiana Centrifugal 89.50 90.70 1.20 



Cuba ^folasscs 91.75 92.45 0.70 



Brazil Muscovados 88.90 90.40 1..50 



Philippine Mats 84.10 86.60 2.50 



Louisiana Molasses 82.60 85.60 3.00 



Louisiana Molasses 74.70 78.40 3.70 



The statement is often made that, inasmuch as raw cane sugars are bought and sold 

 upon the basis of a test which gives less than the true amount of sucrose, an injustice 

 is done to the seller. This statement is made, however, without due consideration of 

 all the facts. The price for a raw sugar is determined almo.st wholly by the yield of 

 pure sucrose which this sugar will give to the refiner. A raw beet sugar, for example, 

 polarizing 93 and containing 1 per cent of ash. is given a value of 88 instead of 93 ; 

 for while the true percentage of sucrose may be very close to 93, the presence of the 

 mineral matter in the sugar reduces its value for refining to the extent of 5 times the 

 amount of a.sh. 



So also with a raw cane sugar which polarizes S2.5. but has a true sucrose content 



