34 SUGAR 



compensator the colours become more uniform, and when 

 an absolute uniformity of colour has been restored he 

 reads off. on the scale the percentage of sugar. This 

 method gives great accuracy, but the instrument has 

 now been superseded perhaps in the interest of those 

 who are colour blind by one in which shadow is sub- 

 stituted for colour, which is said to be still more 

 accurate. 



Thus is the quantity of crystallizable sugar accurately 

 determined in the laboratory. The other varieties of 

 sugar, called uncrystallizable,have an avidity for oxygen ; 

 their quantity is therefore determined by measuring 

 the quantity of a standardized solution of oxide of 

 copper (cupric oxide) which is " reduced " by the 

 sugar solution to the insoluble form of cuprous oxide, 

 which contains less oxygen. The uncrystallizable 

 sugars are therefore called " reducing sugars." They 

 generally exist in the form of equal quantities of dextrose 

 and levulose, which mixture is created by the action 

 of acid and heat on the crystallizable sugar, which is 

 now called sucrose. This mixture is called " invert 

 sugar " because it deflects the polarized ray to the left 

 instead of to the right. 



But dextrose and levulose also exist separate in 

 varying small quantities in the sugar cane. Dextrose 

 is so called because it deflects the ray to the right, but 

 not so much as sucrose. Levulose is so called because it 

 largely deflects the ray to the left. Dextrose is produced 

 in large quantities for industrial purposes by the action 

 of acid on the starch contained in grain, and is called 

 glucose. Maize is generally used for the purpose, and 

 the United States is the largest producer. In that form 

 it is a dull greyish white viscous substance with a 

 sickly-sweetish taste. It is also produced in a solid 

 form. Levulose is also called fructose or fruit sugar. 



