Silk consists of a fibre prepared from the filaments of the cocoons spun by the larvae of Bombyx mori Linn. (Family Bombycidae), the mulberry silkworm, and those of other species of Bombyx and of various species of Antheraea (Family Saturnidae).
Silk is cultivated in Japan, China, France and Italy. It is also cultivated in small quantities in Bangladesh and India.
Preparation of silk:
The cocoons, a covering of filaments produced by the larvae of the silkworm around themselves before passing to their pupal stage, are collected immediately after the larvae reach the pupal stage. They are then baked or steamed to kill the pupae. The cocoons are then placed in hot water to soften and to remove partly the natural gum of the silk filaments. The ends of the filaments from two to six cocoons are then caught up and up winded. A number of these are twisted together to form a single thread of raw silk. This raw silk is made up into hanks for processing into fabrics.
Macroscopical and microscopical characters:
Silk consists of very fine, soft, smooth and solid threads, usually yellow in colour. The threads possess considerable tensile strength. Under the microscope, silk appears as cylindrical or slightly flattened, structureless solid threads, 5 to 25 um in diameter. It is easily soluble in CUOXAM, 66 percent cold sulphuric acid and concentrated hydrochloric acid.
The mass of the silk fibre is made up of the protein fibroin, coated externally by another protein sericin or silk gum, which cements the fibres together. The proteins of silk do not contain sulphur.
The pharmaceutical uses of Silk include the manufacture of ligatures, oiled silk and some sieves.