THE CHEMISTRY OF SUGAR. 501 



Sugar is a general name applied to a class of bodies composed of 

 carbon, oxygen, and hydrogen, having a more or less sweet taste, and 

 exercising a rotatory power on the plane of polarized light. 



In chemical composition the sugars may be regarded as a combina- 

 tion of water with carbon, and they belong therefore to that class of 

 bodies which are known as carbo-hydrates. Starch, wood-fiber, and 

 various sorts of gums are bodies nearly allied in chemical composition 

 to sugar. 



Sugar is chiefly a product of vegetable growth, and is found in 

 some part or other of a large number of substances. 



Sometimes it is found in the root, as in the beet and sweet-potato. 

 Again, it occurs in the fruit, as in the grape and water-melon. At 

 other times it is stored in the juices of the plant, as in the maple-tree 

 and the sugar-cane. 



In whatever position it occurs, it is always diluted with water, and 

 mixed with various gums and albuminous bodies peculiar to the plant 

 containing it. 



The manufacture and refining of sugar consist in separating it 

 from these impurities, and evaporating the water until the crystalliz- 

 ing point is reached, or a sirup is produced. 



I have said that sugar is of vegetable origin. This must be con- 

 strued to mean the sugars of commerce and common consumption. 

 The animal organism possesses a glycogenic function in common with 

 plants. 



The amount of sugar, however, produced by the animal organism, 

 with the exception of that from the milk-glands, is inconsiderable in 

 a state of health. In certain forms of disease, however, as in diabetes 

 tnellitus, the amount of sugar produced in the body may be immensely 

 increased. 



Sugar may also be made by chemical means from the bodies 

 already mentioned, such as starch, cellulose, gum, etc. 



In this sketch I will mention only the more important sugars. For 

 the purposes of a popular classification the sugars may be arranged as 

 follows : 



1. Cane-sugar, or sucrose. 



2. Grape-sugar, or glucose. 



3. Milk-sugar, or lactose. 



4. Starch-sugar, or amylose. 



Cane-sugar, in a commercial sense, is by far the most important of 

 these bodies. 



It has never been formed by chemical synthesis, and the chief 

 sources from which it is derived are the sugar-cane, the sugar-beet, 

 and the sugar-maple. TVhen pure it is a white crystalline body easily 

 soluble in water and having an intensely sweet taste. The molecule 

 of cane-sugar consists of forty-five atoms, distributed as follows, viz., 

 twelve atoms of carbon, twenty-two of hydrogen, and eleven of oxy- 



