SILK. 169 SILKWORM. woods. In making artificial silk from cotton the lint is first carded into wadding, which is im- mersed in a mixture of 15 parts of nitric acid of 1.5 specific gravity and 85 parts of commercial sulpliuric acid. This process transforms the cot- ton into nitro-cellulose and continues until its color, when examined with the microscope and polarized light, is a clear blue. The next stage in the process is to press the nitrated cotton, which is then washed to remove all traces of the acid. It is then dissolved in a mixture of alcohol and ether, forming collodion, which re- quires aging in order to secure the best results. This collodion is placed in steel cylinders and the liquid is expelled by pressure through capillary tubes into nitric acid diluted one-half with water. The fibres tluis produced are wound di- rectly upon reels and are ready for subsequent treatment. This involves the drying of the fibre by warm air and its denitration in a bath of alkaline sulphide. It then goes through addi- tional washing f.nd drying processes, after which it may be spun and dyed like natural silk. The process with wood fibre is quite similar and there has also been an attempt made to produce a similar fibre by drawing gelatin into fine threads. It is said that the elasticity of arti- ficial silk made by the process described is equal to that of the natural silk, while in lustre and brilliancy it is said to surpass the latter. It was claimed at the time that this silk could be pro- duced at from one-third to one-fourth the cost of real silk. Consult Sadtler, industrial Orrjunic Cheiiiistr;/. (Philadelphia, 1900). See SiLK. Compare natural process described under Silk- worm. SILK, Veget.ble. a term usually applied to the fibre which surrounds the seeds of the pods of certain phints of the milkweed family. This fibre is soft and silky and has been employed to mix with silk and with wool in the manufacture of certain fal)rics. See Silk. SILK COTTON TREES. See Eriodendeon. SILK-OAK. See Grevillea. SILKWORM. The 'silkworm' of commerce is the caterpilhir of Bomht/x mori, a moth of the family Bombycida>, a group commonly known as the family of silkworm moths. The caterpillars of all of the species of this group have the silk- glands largely developed, and many of them spin large quantities of silk in making their cocoons. The Bombycid.ne have a very short and rudi- mentary proboscis, live for a very short time in their perfect state, and take little or no food; the body is thick and hairy; the wings are large and broad ; the antennae are pectinated. The caterpillars feed on the leaves and other tender parts of trees or other plants ; the chrysa- lids are inclosed in a cocoon of silk. The com- mon silkworm is a native of either the northern provinces of China or of Bengal. The perfect insect is about an inch in length, the female rather larger than the male, the color whitish, with a broad pale brown bar across the upper wings. The females generally die very soon after they have laid their eggs, and the males do not survive much longer. The eggs are numerous, bluish in color, about the size of a pin's head, not attached together, but fastened to the sur- face on which they are laid by a gummy sub- stance, which, when dry, becomes silky. They are laid about the end of .lane, and arc hatched about the middle of the fidlowing .ijiril, or at the time when the leaves of the mulberry unfold. The caterpillar is at first sm:ill, not more than a quarter of an inch in length, but rapidly increases in size, till, when full grown, it is nearly three inches long. It is usually of a yel- lowish gray color, but some varieties are much darker. The skin is changed four times during the growth of the caterpillar. Before each change of skin it becomes lethargic, and ceases to eat, whereas at other times it is very vora- cious. When the skin is read.y to be cast off, it bursts at the fore part, and the caterpillar then, by continually writhing its body, without moving from the spot, thrusts it backward: but silkworms frequently die during the change of skin. A very rapid increase of size takes place while the new skin is still soft. The natural food of the silkworm is the leaf of the white mulberry, but it will also feed on the leaves of some other plants, as black mulberry and let- tuce, and in the United States it is frequently fed on the Osage orange. When so fed, however, it produces silk of inferior quality. The silk- producing organs are tw^o large glands (seric- teria) containing a viscid substance, which ex- tend along a great part of the body, and termi- nate in two spinnerets in the mouth. These- glands become very large when the change to the chrysalis or pupa state is about to take place. When about to spin a cocoon, the silkworm ceases to eat, and first produces the rough fibre which forms the outer part of the cocoon, and then the more closely disposed and valuable fibre of its interior. In this process the position of the hinder part of the body is little changed, but the head is moved from one point to another ; and the cocoon when finished is much shorter than the body. Each fibre of silk, when examined by a microscope, is seen to be double, being equally derived from the two silk-producing or- gans of the caterpillar. A single fibre ranges from 800 to 1000 yards in length. The time of the silkworm's life in the caterpillar state is about four weeks. About three days are occupied in the spinning of the cocoon; after which about two or three weeks elapse in the chrysalis stage be- fore the perfect insect comes forth. Di.SEA.SES. The silkworm is liable to various diseases, particularly to muscai-dine, p^brine, flacherie, gattine, and grasserie. Muscardine, commonly known as silkw-orm rot, is due to a fungous growth within the caterpillar. A worm so affected becomes of a dull white color, slug- gish in action, and soon dies. A few days after death it becomes hard, red, and floury. The cause of the disease was discovered by an Italian. Bassi, and the fungus is called Botriitis Bas- siana. Pebrine, which unquestionably is a bac- tei'ial disease, is hereditar.v, and probably is contagious and infectious besides. It is the most fatal of silkworm diseases. By 1847 its ravages in France compelled the French to get their silkworm eggs from Italy. The disease spread to Italy and then the eggs were procured from the Danube, then from China, and in 1865 healthy eggs could be obtained only from .Taiiaii. I'asteiir showed that selection and isolation of liealth,y moths is the only remedy. With the methods of isolation and care against con- tamination such as are at present practiced,
