SILK, the peculiar glossy thread spun by the caterpillars or larva of certain species of moths, and a well-known kind of fabric manufactured from it. The chief silk-producing larvae belong to the family of the Bombycidie, of which group the common silk moth, Bambyx marl, is the most familiar species, being that which is by far the most important in artificial culture. This family of moths is distinguished by the small size of the proboscis, by the thick hairy body; and by the large, broad wings. The common silk moth possesses a short body, stout legs, and white wings, which are marked by black lines running parallel with the wing borders. The female moth deposits her eggs in summer on the leaves of the mulberry tree, Monts alba. For hatching artificially the eggs are placed in a rocm heated gradually up to a temperature of about 80° F. In 8 or 10 days the young appear. The caterpillars are then covered with sheets of paper on which mulberry leaves are spread, and make their way through perforations in the paper to the mulberry leaves, their natural food. The leaves when covered with caterpillars are laid on shelves of wicker work covered with brown paper. When first hatched the larva' or worms are black and about inch long. The larval or caterpillar stage lasts from six to eight weeks, and during this period the insect generally casts its skin four times. After casting its last skin the insect is about two inches long, and in 10 days attains its full growth of three inches. The insect's body consists of 12 apparent segments, with six anterior forelegs, and 10 fleshy legs or "prolegs" provided with hooks in the hinder body-segments. The mouth is large, with powerful jaws. At this stage the insect becomes languid, refuses food, and prepares for its next change into the pupa or chrysalis stage.
The Chinese appear to have been the first to render the filamentous cocoon sub stance serviceable to man, and China is still the chief silk-producing country in the world. Before the reign of Augustus the use of silk was little known in Europe, and the culture of the silkworm was not introduced till the 6th century. It was at first confined to Constantinople, but soon spread to Greece and then through Italy to Spain. When the Duke of Parma took Antwerp in 1585 a check was put on its trade in silk goods, and many of the weav ers from Flanders and Brabant took ref uge in England. Revocation of the Edict of Nantes (1685) drove hosts of silk workers into exile, 50,000 settling in Spital fields, London. A silk-throwing machine, constructed on Italian models secretly ob tained, was fitted up at Derby in 1718 by Thomas Lombe (afterward Sir Thomas Lombe), who obtained a patent in 1719, and on its expiration received a grant of X14,000 ($70,000) for his services to his country. In France looms were set up at
Lyons in 1450, and at Tours in 1470. The first nursery of white mulberry trees was founded by a working gardener of Nismes.
In the manufacture of silk the first op eration is the unwinding of the cocoons and the reeling of the silk. For this pur pose they are placed in shallow vessels containing hot water, which softens the gummy matter of the cocoons. The ends of the filaments are then conducted by guides to large reels moved by machinery. Four or five (or more) threads from as many different cocoons are thus brought together, and uniting by the gum form one thread. When the cocoon is half unwound the filament decreases 50 per cent. in thickness. The silk thus produced is called raw silk. Before it can be woven into cloth the raw silk must be thrown. This is often a special trade and is usually conducted by machinery in large mills. Previous to throwing, the silk is carefully washed, wound on bobbins, and assorted as to its quality. In the throwing ma chine it is again unwound from the bob bins, twisted by the revolutions of a and then wound on a reel.
The cultivation and production of silk a was commenced in the United States at a a very early period. In 1734 eight pounds of silk cocoons raised in Georgia were taken to England by Governor Oglethorpe.
Nearly a century afterward the first silk made by machinery in the United States was manufactured at Mansfield, Conn. (1829). Silk cultivation is now a firmly established industry in California and several other States, and there are extensive silk manufactories at Paterson, N. J., Hartford and South Manchester, Conn., Newton, Groton, Northampton and other points in Massachusetts, Philadel phia, Baltimore, New York, etc. Sewing silks of American manufacture are re garded throughout the world as superior in many respects to those manufactured in Italy or elsewhere in Europe. The same is also true of American-made dress silks and ribbons. The silk crop of the world in 1919 was about 24,100,000 kilos, of which the greater part came from Ja pan. The production of American fac tories in the same year was valued at $750,000,000, compared with a value of $250,000,000 in 1914. The imports of manufactures of silk in the United States in 1920 were valued at $87,728,181.