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SILICA

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SILKWORM

he had no other heir. The three Silesian Wars (1740-42; 1744-45; and 1756-63-— the Seven Years War) ended in securing Silesia to Prussia, except the Austrian province of Silesia, a country south of Prussian Silesia, covering 1,987 square miles, rich in mines and with a population numbering 756,949.

Silica (sil't-ka). a compound of silicon and oxygen (SiO2), is found in the pure state in the form ot quartz or rock crystal. Flint, sandstone and chalcedony are nearly pure silica. It occurs also in combination in a large number of abundant minerals which are called silicates, and of which feldspar, mica, hornblende and clay are examples. Silica exists in many plants, particularly the grasses, in the quill-feathers of birds and in sponges. Most animals contain very little of it. Silicon, the nonmetallic element contained in silica, is never found in the free state. Although, next to oxygen, the most abundant element in the earth's crust, it is merely a chemical curiosity, being very difficult to separate from oxygen. Silica is largely used in making glass, and is an important constituent of porcelain, china, bricks etc.

Silicic (stl'Z-k'l), a short silique, the peculiar fruit of the mustard family. See FRUIT.

Silique ( stl'lk), the peculiar pod-like fruit of the mustard family, characterized by a false partition which runs lengthwise and divides the pod into two chambers. See FRUIT.

Silk, the cloth and thread manufactured from the fiber obtained mostly from the cocoons of the silkworms. The making of silk probably originated in China, trie wife of an emperor being credited with first unwinding a silk cocoon in 2600 B» C. The silkworms' eggs were brought to Constantinople from China about 552 by two Persian monks, who carried them in a hollow cane. They were successful in raising them and in introducing the manufacture of silk. The new industry spread through Greece, was carried into Sicily by prisoners of war, and brought to Spain by the Moors. Louis XI and Francis I imported workmen from Milan into France, and succeeded in starting the silk-manufacture after the cultivation of the mulberry tree for food for the worms had been established in 1564. In England silk-manufacture began under James I, but received a powerful impulse in 1685, when a large number of silk-weavers were driven to England by the Edict of Nantes. James I nade an effort to introduce the industry into the American colonies, sending eggs to Virginia and offering rewards for their cultivation, but tobacco was more profitable. It was cultivated in South Carolina and Connecticut before the Revolutionary War. There have been several efforts to make the cultivation of the silkworm more general in the United States, one in California in

1854 and a Woman's Association formed in Philadelphia in 1876, but with no great result. The manufacture of silk is, however, carried on quite extensively, the center of the industry being Paterson, N. J., where there are more than 100 silk-factories. France is the principal silk-making country, the British silk-trade having been much injured by the introduction of French goods free. The process of manufacture takes tli£ raw silk, obtained from the cocoQns of the worm, by winding it off through a reeling-machine; cleans, twists and doubles the threads; and winds them on bobbins and reels for the weaver. There is a considerable amount of waste in all the processes, which, known as waste silk, was for a long time considered useless, but in 1857 a method of spinning yarn out of this waste was invented by Lister of Bradford, England, which has added very much to the industry. The process of weaving silk from the prepared thread resembles that of weaving cotton or woolen goods.

Silk'worm, any larva or caterpillar which produces a silken cocoon used in the manufacture of silk. The name applies especially to the famous silkworm (Bom-byoc mori) that feeds on the mulberry tree. All silkworms are the larvae of moths. Their eggs are laid to the number of 200 or 300 by a single indi-v i d u al. On hatching, the caterpillars go through several moults. They eat ravenously save just before moulting, and many die during the change of skin. Silkworms are subject to various diseases, great numbers being attacked by a fatal fungous disease. Constant care must be used in rearing them, and strict attention paid to cleanliness, ventilation and temperature. When they reach the fifth stage they eat enormously, and attain a length of three or three and one half inches. They now are naked* worm-like animals of a pale greenish color. About 36 days or more after hatching, they begin the formation of the cocoon, in which they undergo the transformations that convert them into moths. The cocoons are the source of the silk. They usually are white or yellowish and about an inch or more long and half as broad. The silk comes from a pair of long, tubular glands which open upon the lower lip of the animal. As the material of a spider's thread hardens on contact with the air, so this silk substance is formed into a delicate strand,.

SILK-WORM, LARVA, CHRYSALIS AND  COCOON