Starch is the form in which food is stored up in the plant for future use. In the seed, it furnishes the material for the growth of the embryo, before it can draw its nourishment from the earth and the air. It sometimes surrounds the embryo, as in the seed of the onion (Figure 26); and sometimes it is found in the cotyledons, or seed-leaves, of

Fig. 26.

the embryo itself, as in the seed of the bean (Figure 27). When the seed germinates, the

Fig. 27.

starch is dissolved, and converted into dextrine, and this into sugar, which is even more soluble. It is then dissolved in the sap, which conveys it wherever it is needed for the growth of the infant plant. Several forms of starch are extensively used as articles of food. Arrowroot is obtained from the roots of a tropical plant, which is cultivated in the West Indies, especially in Bermuda and Jamaica, and to some extent in the East Indies and in Africa. Tapioca is also made from the roots of plants which grow in the West Indies, South America, and Africa. Sago is extracted from the pith of several species of palm-tree, in India and the islands of the Indian Archipelago. Cornstarch, maizena, and farina, and various other preparations of the kind, are made from the starch of Indian corn, wheat, etc. Potatoes yield from 12 to 27 per cent of starch; peas and beans from 33 to 36 per cent; wheatflour, 56 to 72 per cent; rye-meal, 61 per cent; maize, 81 per cent; rice, 83 to 85 per cent.

Starch is also used in large quantities for laundry purposes; in the manufacture of cotton cloth, as a sizing for the thread; and in the making of dextrine and grapesugar (161, 162).

159. Sugar.- Sugar, like starch, is a vegetable product, prepared for the future growth of the plant. It is found, dissolved, in varying proportions, in the juices of all plants. In ripe fruits it is quite abundant; pears containing 6 per cent; peaches, 16 per cent; and cherries, 18 per cent. In rye-meal there is about 3 per cent of sugar; in wheat-flour, from 4 to 8 per cent; in beet-root, from 5 to 8 per cent; and in dried figs, more than 60 per cent.

There are many kinds of sugar, of which the two most important are cane-sugar and grape-sugar.

160. Cane-Sugar. -Cane-sugar, C12H22O11, is found in the juices of many plants. It is mostly prepared from the juice of the sugar-cane; but on the Continent of Europe, it is largely made from beet-juice. In tropical regions, it is also manufactured from the juice of the date-palm; and in the Northern United States it is obtained in considerable quantities from the sap of the rock or sugar maple.

In the manufacture of sugar from sugar-cane, the juice is first extracted from the canes by pressure, then mixed with a small quantity of slaked lime, and heated nearly to boiling. The lime serves to neutralize the acid in the juice, and also to remove the albuminous matter, which, if left in the sugar, would soon cause it to ferment and spoil. The juice is next evaporated in open pans to a thick syrup, which is allowed to cool and crystallize, and is then drained in perforated casks. The liquid drained off is known as molasses.

By this process, raw or brown sugar is obtained. This is refined by dissolving it in water, adding albumen (usually from ox-blood), and heating it. The albumen separates most of the impurities from the solution, which is then filtered through bone-black to remove the coloring matter. It is then boiled down in vacuum pans, large

vessels from which the air is partially exhausted by pumps, in order that the evaporation may be carried on at a lower temperature than in open pans. By this process there is a saving of fuel, while the quantity of sugar obtained is increased. The concentrated syrup is crystallized in conical moulds, with an opening at the bottom for drainage, and thus becomes loaf-sugar.

When sugar crystallizes very slowly, it forms the large and very hard crystals seen in rock-candy. In making loaf-sugar, the syrup is frequently stirred, to prevent the formation of these large crystals.

If cane-sugar be heated to about 400°, it loses two atoms of water, and is converted into caramel, a dark brown substance, much used for coloring brandy and other spirits.

For several

The manufacture of sugar from the sugar-cane, and other sources, is now one of the largest branches of human industry, but its importance is of comparatively modern date. Sugar was known to the Greeks and Romans only as a medicine or a curiosity. centuries after the Augustan age, we find scarcely any mention of it; and, even so late as the seventh century, Paul of Ægina describes it as "India salt, resembling common salt in color and consistency, but honey in taste and flavor." The sugar-cane appears to have been introduced into Europe by the Saracens, who cultivated it in Rhodes, Cyprus, Crete, and Sicily, in the ninth century. In the fifteenth century, it was transplanted into Madeira and the Canary Isles, whence it was probably brought to America. It became known in England in the fourteenth century; and, in 1329, it was sold in Scotland at one ounce of silver (equal to four dollars of our money) a pound. It did not become an article of ordinary consumption until the beginning of the seventeenth century. Since that time its use has very rapidly increased, and it

seem's destined to an indefinite extension. "It is so nutritious, wholesome, and agreeable, that there never can be a limit to its use, except in a prohibition or an inability to buy it. Men and nations differ widely in respect to most kinds of food, sauce, and drinks. Neither wheat, rice, flesh, nor potatoes can command unanimous favor. No article of housekeeping, save sugar, can be named, which is so universally acceptable to the infant and the aged, the civilized and the savage."

The annual production of sugar throughout the world is estimated at more than 5,000 millions of pounds, of which nearly 88 per cent is cane-sugar; about 7 per cent, beet-sugar; 4 per cent, palm-sugar; and about I per cent, maple-sugar. According to Chambers's Encyclopædia (1867), the yearly consumption for each inhabitant, in several great countries, is as follows: Russia, 11⁄2 lbs.; Austria, 1 lbs.; France, 4 lbs.; Belgium, 6 lbs.; Great Britain, 30 lbs. ; United States, 40 lbs.

161. Grape-Sugar. - Grape-sugar, or glycose (less properly spelled glucose), C12H24O12, is found in the juice of grapes, plums, cherries, figs, and many other fruits, and may often be seen in a crystalline form on raisins and dried figs. It likewise occurs in honey.

It is manufactured on a large scale, in Europe, from starch. A mixture of starch and water, at a temperature of about 130°, is made to flow gradually into a vat, containing boiling water, acidulated with one per cent of sulphuric acid. In about half an hour, the starch is converted into sugar. The sulphuric acid is neutralized with chalk, forming a deposit of calcic sulphate; and the clear solution of sugar is then boiled down and crystallized. Instead of starch, in this process, paper, flax, cotton and linen rags, sawdust, or any other form of woody fibre, may be used. The woody fibre is first converted into starch, and then into sugar.

Glycose is largely used in Europe for confectionery, for adulterating cane-sugar, and for the manufacture of beer and spirits.

162. Dextrine.-Dextrine, or British gum, C12H20O10" is obtained by heating starch to about 400°; or by subjecting the starch to the long-continued action of dilute acids, at a high temperature. It is often used instead of gum-arabic in calico-printing, and for stiffening certain goods. It is also applied to the back of postage-stamps and other adhesive labels.

When wheaten bread is baked, a small quantity of starch is converted into dextrine on the outside of the crust, forming a brownish glazing.

163. Cellulose and Gun-Cotton.— Cellulose, or woody fibre, C12H20O10, has already been described (150). It is insoluble in water, alcohol, or ether, but dissolves in an ammoniacal solution of cupric oxide (oxide of copper).

Gun-cotton, or nitro-cellulose, is made by the action of strong nitric acid upon cellulose. Cotton wool is immersed, in small portions at a time, in a mixture of equal volumes of strong nitric and sulphuric acids. It does not undergo any apparent change; but, on being washed and dried, it is found to be very inflammable. Six atoms of its hydrogen have been replaced by NO2, so that its composition is now represented by C12H14 (NO2)8O10*

The use of gun-cotton, as a substitute for gunpowder, has been proposed, for the following reasons:

(1) The explosive force of gun-cotton is, weight for weight, greater than that of gunpowder. (2) The products of the combustion of gun-cotton, being chiefly carbonic acid and nitrogen, are not so apt to foul the gun. (3) When moistened, it becomes inexplosive, and only requires drying to render it again explosive.

The reasons which render the general adoption of this substance doubtful are,—(1) its liability to explode on