英文科學(xué)讀本 第五冊(cè)·Lesson 32 Vegetable Secretions—Sugar

Lesson 32 Vegetable Secretions—Sugar

It will be readily understood, from the rapid growth they make, that plants are, as a rule, gross feeders. Yet each plant takes up from the soil only that which is required for its own special needs—nothing more. From this earth-food it elaborates, by means of its leaves, its own special secretion. Hence it is that the sap of the one plant becomes a sweet, sugary juice; while that of another yields camphor; a third gives resin and turpentine; others india-rubber and gutta-percha. One of our recent lessons introduced a number of plants whose sap is elaborated into oily matter, and stored away in their fruit or seeds. We shall now proceed to study these vegetable secretions briefly, commencing with sugar, as perhaps the most important of all.

All the varieties of sugar known in commerce are called by one common name—cane-sugars. They do not all come from the sugar-cane, although that plant is still one of the chief sources of our sugar supply. Besides that obtained from the sugar-cane, there are other preparations known as beetroot sugar, and maple sugar, maize, and palm sugar. The common name, cane-sugar, is given to all of them, because in their properties they all resemble the sugar of the sugar-cane.

There are many varieties of the sugar-cane under cultivation in different parts of the world, each being peculiarly adapted to its own locality, climate, and soil. Originally a native of the Old World, it was introduced into America by the Spaniards in 1520. It is now extensively grown in the United States, Brazil, and the West Indies, as well as in India, and Mauritius, and the East Indies.

The plant itself is one of the grass family, and its cultivation is simple. The young plants are raised from cuttings, and not from seed, as the sugar-cane is rarely allowed to mature its flower, and so ripen its seeds. The plants take from twelve to fifteen months to reach their full growth. The stem is then a thick, stout, jointed cane, from 8 to 12 (and even in some varieties, 20) feet in height. The stems of most grasses are hollow; the sugar-cane is a solid stem. The juice, which contains about 15 or 20 percent sugar, resides in the central pith of the stem.

As the canes ripen, the flowers begin to appear, and it is then time to cut them down, A sugar plantation, towards harvest time, with its yellow, striped, or purple-tinted stems, surmounted by immense bunches of feathery lilac and rose-colored flowers, presents a very beautiful and attractive sight, especially to one who looks on it for the first time.

The canes usually ripen about March or April, and the sugar harvest then begins. Men pass along between the rows and cut them down with large knives. Each cane is then divided into short lengths, the natural joints of the stem being preserved as cuttings for future planting. The divided canes are next carted to the sugar-mill, where the juice is extracted by pressing them between heavy iron rollers. It is estimated that the average yield of the trimmed canes is from one to three tons per acre, and it takes the juice of twelve or fourteen tons of canes to produce a hogshead of sugar. The sugar harvest is the great season of the year for the people of those countries where the canes grow. To them, and especially during harvest time, the sugar-cane becomes a staple article of food. Men, women, and children suck and chew the ripe stalk; many Black people practically live on it, and get fat, during this time.

The raw juice contains not only sugar, but a considerable amount of gluten. Hence it is in all respects a true food, capable of supporting life and animal vigor.

This gluten has to be removed from the juice, or it would act as a natural ferment, and turn the sugar into an acid. This is done by adding a certain quantity of quicklime to the juice; the lime combines with the gluten, and carries it to the bottom of the vessel. The juice, thus clarified with the aid of the lime, is first filtered, and then boiled rapidly down in large copper boilers. The impurities rise as a thick scum to the top during the boiling, and must be carefully skimmed off from time to time. Indeed, the whole process of boiling is an important one, and requires great care to prevent the juice from burning or blackening. The crushed canes themselves provide the fuel for this part of the work.

The water is gradually evaporated, while at the same time the juice thickens into a syrup. When it is sufficiently thick, this syrup is run off into wooden vessels to cool. As it cools it separates into crystals, and in this state it is put into casks, perforated with holes, to drain. The liquid portion of it, that refuses to crystallize, drains off into vessels placed below, and is known as molasses or treacle.

Beetroot sugar is obtained from a variety of the beet plant known as the sugar-beet, which contains as much as one-eighth part of its weight of sugar. The sweet juice is easily extracted from the beetroot, and when boiled and refined it has all the properties of cane-sugar.

Beetroot is extensively grown for its sugar in France, Belgium, Russia, Germany, and other countries of Europe. In fact, beetroot sugar is commonly known as European sugar. In each of these countries the manufacture of beet-sugar forms a most important industry.

Maple sugar, or, as it is sometimes called, North American sugar, is obtained from the sap of the sugar-maple, a large, handsome tree, which often attains the height of 60 or 80 feet. The tree is a native of Canada and some parts of the United States, especially of those regions where extensive natural forests of maples flourish.

The sap of the tree is very sweet; it contains the same kind of sugar as the sugar-cane. The sap begins to flow in February, and, when March comes, parties of sugar-makers start for the forest. They make incisions into the trunks of the trees, and place small buckets below to catch the sap as it flows. To assist the flow of the sap into the buckets, they usually fit into the holes little pipes made of elder shoots. The sap is collected twice a day, and boiled on the spot in large boilers. Two or three men can usually make, in the season (March and April), as much as 4000 or 5000 lbs. of sugar.

The people of Central America make another variety of sugar from the green stalks of corn.

These, if boiled, yield a sugar having all the characteristics of cane-sugar. It is known as maize sugar, or Mexican sugar.