APPENDIX 
455 
consisting of two very fine strands or “ brins,” composed of structureless (colloidal) 
translucent “ fibroin ” cemented together by a waxy, glue-like material “ sericin.” 
The double filament of the raw silk is technically termed “ have.” It is customary 
to unite the have from S to 15 cocoons in the process of reeling the silk. This com¬ 
pound fiber is known as “ raw silk.” Silk fabrics are produced through sub¬ 
sequent treatment of the raw silk, or from the waste obtained in reeling which has 
been spun. Under the microscope silk has the appearance of single fine structure¬ 
less filaments, rarely striated longitudinally and in cross-section irregularly oval. 
Polarize strongly with brilliant colors. 
Tussah or Wild Silk. — A term applied to silk obtained from a variety of species 
of silk worm other than S. mori. A few of these have been reared in captivity. 
Chinese “ Tussah ” silk is usually obtained from Antheraa pernyi and that from 
India from A. mylitta. Tussah silks are usually brownish in color, producing fabrics 
of which “ Pongee ” silks may be considered the t5q)e. Microscopically, wild 
silk consists of flattened, ribbon-like filaments, of much greater diameter than 
mulberry silk, with many fine longitudinal striations and where the fibers have 
crossed one another in the cocoons, while soft, an impression is left on each fiber. 
These impressions are usually oblique to the axis of the fiber and are visible under 
the microscope as distinct cross-striations, accompanied by a slight increase in 
the diameter of the fibers at these points, thus producing in the filament a some¬ 
what wavy outline and a variable breadth. In cross-section the fibers are seen 
to be flattened and more or less triangular in outline. Polarize strongly with 
high colors if thick. 
GROUP E. ARTIFICIAL OR “ FIBER ” SILKS. 
A number of very different processes have been developed and placed upon a 
commercial basis within a comparatively few years. In the United States three 
types of artificial silk are being manufactured upon a commercial scale at this 
date (1921). 
Viscose Silk. — (Alkali-Cellulose Xanthate or Thiocarbonate.) Said to be 
obtained by the action of caustic soda and carbon bisulphide upon wood pulp, 
which has been previously treated with caustic. The jelly-like material thus 
obtained is clarified and forced through minute orifices into a concentrated ammo¬ 
nium sulphate solution or into dilute sulphuric acid and thus coagulated. 
Under the microscope viscose silk filaments are seen to consist of broad thick 
ribbons, scored with deep longitudinal striations and ridges. Air and solid inclu¬ 
sions are apt to be quite numerous. The filaments yield cross-sections varying 
from irregular ovals, lenticular or crescent-shaped figures to those with parallel 
sides and rounded ends. The filaments polarize strongly. 
Liisiron Silk. — (Cellulose acetate). Obtained by treating hydrocellulose with 
acetic anhydride and sulphuric acid. The cellulose acetate is dissolved in a sol¬ 
vent such as chloroform, acetic acid, ethylacetate-alcohol, etc. The thick viscous 
material is forced through orifices into water. 
The filaments are finer than viscose, transparent, structureless, with only fine 
striations, are of quite uniform diameter and in cross-section are somewhat flattened 
ovals. Only with careful illumination and focusing may the very fine, almost 
invisible, longitudinal striations be discovered. Filaments polarize very feebly. 
