HYDROCARBONACEOTJS SUBSTANCES. 59 



boiling alkalies, in reducing the Copper-oxide in Trommer's and Fehling's 

 and in undergoing the alcoholic fermentation by the influence 

 of yeast. It enters into fermentation, however, very slowly, as com- 

 pared with glucose, and the process is usually incomplete. In the 

 fermentation of milk, a part of its sugar is converted into lactic acid, 

 C 3 H 6 3 , also a carbo-hydrate. By boiling with dilute sulphuric or 

 hydrochloric acid, lactose becomes readily and completely fermentable. 

 This sugar forms an important element in the food of the infant, in 

 which it is a constant ingredient. It is formed in the mammary gland, 

 probably by transformation from glucose, but the exact method of its 

 production is unknown. It is discharged with the milk, as a reserve 

 material for the nutrition of the infant. 



3. Saccharose, C 12 H 22 O U , Cane Sugar. 



This variety, the oldest known species of sugar, is derived from the 

 juices of the sugar-cane, where it exists in great abundance. It 

 solidifies, on cooling from a hot concentrated solution, in white granular 

 crystalline masses ; the form in which it is generally used for culinary 

 purposes. If crystallized more slowly it furnishes large, colorless, 

 prismatic crystals, known as ''rock candy" or "sugar candy." This 

 sugar is also obtained from the juices of the beet-root, and, im- 

 perfectly purified, from those of the sorghum and the sugar-maple. It 

 exists to some extent in the green stems of Indian corn, in sweet 

 potatoes, in parsnips, turnips, and carrots, and in the spring juices of 

 the birch and walnut trees. Honey is a mixture of glucose and saccha- 

 rose with various other substances. 



Cane sugar originates from glucose, in the process of vegetation, by 

 a change the reverse of that by which glucose is formed from starch, 

 that is, by dehydration. A comparison of the chemical composition of 

 the two substances will show the manner in which the transformation 

 takes place, namely : 



GLUCOSE. WATER. CANE SUGAR. 

 2(C 6 H 12 6 )-H 2 = C 12 H 22 11 . 



Saccharose is the most soluble of the sugars, and has the strongest 

 sweet taste. It rotates the plane of polarization to the right 73. 84. 

 It differs from glucose by the fact that it is not turned brown by boiling 

 with an alkali, and does not reduce the copper-oxide in Trommer's test. 

 It may be converted into glucose, however, by a few seconds' boiling 

 with a dilute mineral acid, and will then react promptly with boiling 

 alkalies and with Trommer's test. Cane sugar is not immediately 

 fermentable, but by contact with yeast it is after a time changed into 

 glucose, and finally enters into fermentation. In the living vegetable 

 tissues it represents a reserve material, and is subsequently reconverted 

 into glucose for the purposes of nutrition.* When taken as food, it is 

 transformed into glucose by the intestinal fluids. 



* Mayer: Agrikultur-Chemie. Heidelberg, 1871. Band I., p. 1>. 



