SILK 



5382 



SILK 



hungry, and soon consume about their own 

 weight of chopped mulberry leaves as a daily 

 ration. Naturally, they grow with great rapid- 

 ity, and cast their first skin after a period of 

 about ten days. This process is repeated about 

 four times during a period of six weeks, when 

 the caterpillar is ready to spin its cocoon. It 

 is then three inches long and half an inch in 

 diameter. The body is in twelve segments and 

 is supported by three pairs of true legs and five 

 pairs of hooked prolegs on the hind segments. 



The caterpillar now ceases to eat and pres- 

 ently begins spinning its cocoon. In a natural 

 state, it sews two leaves together and spins the 

 cocoon between them; but under cultivation, 

 the worm is supplied with a rack containing 

 numerous small cells, to the sides of which the 

 cocoon is attached. The outer covering, or 

 floss, is first spun, and then the silk is wound in 

 a continuous thread about the body, the worm 

 shrinking in size as it thus spins out its sub- 

 stance. The film is formed from a gluelike ma- 

 terial secreted in two glands, one on either side 

 of the body, connecting with an opening in the 

 upper lip called the spinneret. The sticky fluid 

 hardens on contact with air; under the micro- 

 scope, it appears as a thread of two strands. 

 This thread is sometimes 1,000 yards long; 

 more often, the length does not greatly exceed 

 500 yards. If left undisturbed, the pupa will 

 hatch in two or three weeks, boring its way 

 through the shell and emerging as a small, white 

 moth. In cocoons from which silk is to be 

 drawn, the insect is killed before it attacks its 

 silky sheath. This is accomplished by placing 

 the chrysalis in a hot oven, exposing it under 

 glass to the rays of the sun or subjecting it to 

 a steam bath. 



The cultivation of the silkworm dates in 

 China from a most ancient period; according 

 to Chinese authorities, it was begun as early as 

 2600 B.C. China is still the chief source of 

 the world's supply of silk fiber, but growing 

 the silkworm is now an important .industry in 

 Japan, Italy, Anatolia, Syria, France and Spain. 

 In the United States, the manufacture of silk 

 has been vastly more important than the pro- 

 duction of the raw material. Silkworms were 

 introduced into the colonies early in the eight- 

 eenth century and cultivated rather extensively. 

 Disastrous speculative activity, together with 

 a blight suffered by the mulberry trees in 1844, 

 dealt the industry a blow from which it has 

 not recovered. 



Process of Manufacture. To facilitate the 

 removal of the filament, the cocoon is steeped 



in warm water, which softens the gum and frees 

 the thread. The double strand spun by the 

 silkworm not being tenacious enough for com- 

 mercial purposes, several filaments are run to- 

 gether through metal or porcelain guides, or 

 eyes, and these adhere to form a single thread. 

 From the guides, the silk is wound upon reels 

 from sixty to ninety inches in diameter, and 

 this is the so-called "raw silk" delivered to the 

 manufacturer in hanks. 



Throwing. Silk goes through what is tech- 

 nically known as a throwing process in prepara- 

 tion for the loom. It is heated in soapy water 

 for several hours. It is then dried, stretched 

 upon reels and wound upon bobbins, dirt being 

 removed and any imperfections in the thread 

 noted in the process. This thread, known as 

 "singles," is frequently used for warp in weav- 

 ing light fabrics. Singles are reeled into large 

 hanks, and these hanks are bound into bundles 

 called "books." In this form a great part of 

 the Asiatic silk reaches America and Europe. 



Doubling. Doubling is accomplished by 

 twisting two or more threads together on a 

 bobbin. The resulting silk, known as tram 

 silk, forms the woof in weaving. Organzine, 

 which is used for the warp of heavier fabrics, 

 is made by twisting two or more single threads 

 separately in the same direction and then 

 doubling and retwisting them in the opposite 

 direction. 



Scouring and Dyeing. When silk emerges 

 from the throwing machine, it has still too 

 much of the natural gum adhering to the 

 strands. This is removed by boiling in a solu- 

 tion of hot soap. In addition to removing the 

 superfluous gum, scouring prepares the silk to 

 take the most brilliant hues in dyeing. In the 

 process, however, it loses from twenty-five to 

 thirty per cent of its weight, and this loss has 

 resulted in the use of still another process, 

 known as loading. Certain chemicals enable the 

 silk to hold more coloring matter, so that it has 

 been found possible to load black silk up to 

 900 per cent of its weight. Commonly the load- 

 ing is, of course, much less than this. Load- 

 ing is defended by manufacturers, but it un- 

 doubtedly lessens the durability of the silk. 



Waste. The waste in silk is very consider- 

 able. This results from the fact that only 

 about seven-tenths of the filament can be un- 

 wound from the cocoon. This waste, together 

 with the coarser flossy covering of the cocoon 

 and the silk taken from cocoons .from which 

 the insect has been allowed to escape, is now 

 treated much like wool. Impurities are re- 



