56 LESSONS IN CHEMISTRY. 



69. Gum is another substance which exists in several 

 plants in considerable quantities. You are familiar with it 

 as exuded from the stems of the cheiTy, plum, and other 

 trees, and also with a kind of it sold in this country under the 

 name of gum arable, and which is procured from a plant 

 of the acacia family, a native of Africa. There are two 

 vaiieties of gum procured from plants: one, soluble in cold 

 vmter and becoming a jelly or mucilage, like gum arable; and 

 another, represented by the gum of the cherry-tree, soluble in 

 boiling but insoluble in cold loater. Both kinds of gum, like 

 starch, dextrin, and cellular fibre, contain carbon united with 

 oxygen and hydrogen, the gases existing in the proportions 

 in which they foim water. 



70. Mucilage. There is another substance, termed muci- 

 lage, resembling gum in its composition and several of its 

 properties, which is found in the root of the common mallow, 

 in linseed, and other oily seeds. It does not, however, like 

 gum, dissolve in boiling water, but merely swells out in bulk. 

 Like starch, it can be converted into sugar by the action of 

 vitriol. 



7 1 . Sugar, the characters of which are so well known, exists 

 in the juice of several plants in great abundance, so that its 

 extraction is a valuable branch of industry. Among the 

 plants famiHar to us in this country, the beet-root affords the 

 largest amount of sugar, and in France is extensively culti- 

 vated for its manufacture. It exists also in small quantity in 

 the juice of the turnip and parsnip, and in ripe fruits, and its 

 presence may be detected by the taste in the clover and young 

 corn. There are several varieties of sugar, the principal of 

 which are, cane sugar, extracted from the sugar-cane of our 

 colonies, and grape sugar, which is met with in the dried 

 raisin, in the apple and other fi'uits, and in honey. It is into 

 grape sugar that starch and the other forms of vegetable 

 matter are converted by the action of the chemical means 

 that I have described. 



72. There are also pecuhar varieties of sugar found in 

 manna, in liquorice, and in the juices of several plants, which 

 differ slightly in composition and properties from those I 

 have mentioned; but the two chief kinds, cane and grape 

 sugar, contain oxygen and hydrogen united, and carbon nearly 

 in the same proportion as in starch and gum. 



73. Albumen. By gi'atiug a potato as already described, 



