FOODS 107 



trace to 2 per cent. Glucose, not more than o-i per cent in 

 refined, or 2 per cent in raw. Saccharose or sucrose, 93 per 

 cent upwards. Other organic matter. Mineral matter. 

 Colouring matter. Sugar mite (Acarus sacchari). 



Moisture. Dry 5 grm. in air-oven at 105 C. to a 

 constant weight (about two hours). 



Ash. Treat residue with pure sulphuric acid and ignite 

 to whiteness (takes twenty minutes). Nine-tenths of the 

 sulphated ash are taken as the true ash. The ash of sugar 

 consists of salts of potash and soda, lime, alumina, and silica. 



Glucose. Estimate by Fehling's solution, volumetrically 

 or gravimetrically. 



Saccharose, or Sucrose, is estimated either (1) directly, by 

 the polarimeter (saccharimeter), or (2) after " inversion," 

 with Fehling's solution. 



1. Polarization is employed in all commercial transactions, 

 and for the assessment of duty by the Customs authorities. 

 It depends on the optical property of some bodies to 

 rotate the plane of polarized light. The specific rotatory 

 power of an optically active substance is the amount of 

 angular rotation (in degrees) of the ray of polarized light 

 which is produced when a solution of the substance con- 

 taining 1 grm. per c.c. is examined in a column 1 decimetre 

 (100 m.m.) long. If a be the observed angle of rotation 

 in the sample, p the weight of the substance per 100 c.c. 

 of solution, / the length of the tube in decimetres, and d 

 the sodium light, then the specific rotatory power (A) d is 

 determined from the formula 



... a 100 X a , 100 X a 



(A) - r^jj^o - t^f p = i maj; 



To determine (A) d for pure cane sugar, dissolve 10 grm. 

 in water and make up to 100 c.c. Put some of the solu- 

 tion in a polarimeter tube, examine, and substitute in 

 formula. Now examine sample similarly and compare 

 results. The ratio of these, multiplied by 100, gives the 

 percentage of pure sugar. Or, in the formula, simply 

 substitute already ascertained values for (A) d , 



+ 66-5 being taken for saccharose, 

 + 52-7 ,, ,, dextrose, and 



95-5 laevulose 



