VEGETABLE PRODUCTS. 151 



of plants with more or less of the nitrogenous compounds and 

 mineral salts. That obtained from the sugar-cane is the most 

 highly esteemed. The juice is pressed out between cylinders, 

 and must soon be boiled with a small quantity of lime to destroy 

 the effect of the nitrogen compounds, which would otherwise 

 produce fermentation. It is then evaporated, and crystallized, 

 and then called Muscovado sugar. It is afterward more or less 

 purified, forming various kinds of white sugar. The plants are 

 said to require, for their perfect maturation, a year or fourteen 

 months. 



Fruit-sugar, C 12 . H^, O l2 . An uncrystallizable sugar, found 

 in sweet fruits, in connection with grape-sugar. 



292. Grape-sugar, C 12 , H, 2 , 0, 2 -f-2 OH [Starch-sugar, Glu- 

 cose). It occurs in the juices of many plants, and in the product 

 of the action of diastase or sub-acid on starch. It gives sweet- 

 ness to most fruits that contain acids. It gives sweetness to all 

 fermented liquors. It is this sugar alone that undergoes fer- 

 mentation, and when materials containing su^ar ferment, the 

 sugar is first converted into grape-sugar by the action of the 

 ferment. 



293. Oils. There is a variety of substances that come under 

 this head that are yielded by vegetables, which agree in certain 

 important particulars. 



Fixed Oils. The fixed oils occur mostly in the seeds, espe- 

 cially in the cotyledons of the embryo : sometimes, however, 

 in the pericarp, as in the olive. Oils are generally divided into 

 greasy oils, or those that wall not dry, and dry oils such as will 

 form a hard varnish. 



This difference in their character is owing to the acids which 

 enter into their constitution. The acid in the non-drying oils is 

 called oleinic, and the drying olinic. These acids have a great 

 tendency to absorb more oxygen, and this is sometimes so great 

 as to set fire to the materials w r ith which they are in contact ; 

 hence manufactories have been burned. 



The common drying oils are linseed-oil, hemp-oil, poppy-oil, 

 nut-oil, &c. 



The greasy oils are olive-oil, almond-oil, rape-seed oil, &c. 



294. These oils occupy cells with a greater or less amount of 

 mucilaginous substance, which in the drying oils prevents the 



What is Muscovado sugar ? What is fruit-sugar? — 292. Constitution of 

 prape-sugar? Where does it exist? To what does it give sweetness? 

 When is cane-su^ar converted into grape-sugar? — 293. Where do fixed 

 oils occur mostly ? How are fixed oils divided ? To what is the difference 

 owiny? What "is the acid in greasy oils ? In drying oils ?— 294. Where 

 are the oils found ? 



