Pauly Silk.—The success of this process aroused the interest of other chemists, and before long several rival processes came into existence, also based on the use of a viscous solution of a cellulose compound. One company, making the so-called Pauly silk, utilized the solvent action of an ammoniacal copper solution upon cellulose for their starting point.
Elberfeld Silk, Glanzstoff.—The Farbenfabriken von Elberfeld, famous manufacturers of dyestuffs, took up the manufacture of silk from a solution of a compound of cellulose with acetic acid; and the Elberfeld silk, or, as it is widely known in Germany, Glanzstoff, is every year becoming a more and more important factor in the silk business.
Viscose Silk.—A still different process, which during the past two or three years has been successfully introduced into the United States, depends upon the curious substance called Viscose, a thick, sticky solution of cellulose made by first treating wood pulp, cotton or other vegetable fibre with strong caustic soda and then dissolving the resulting product in carbon disulphide.
This Viscose was first introduced for many different purposes. The solvent, carbon disulphide, is very volatile, and flies off readily, leaving the cellulose behind in the form of a stiff jelly which, on drying, becomes solid and strong. So Viscose was used for water-proofing paper, etc., for making solid articles like piano keys and billiard balls, and even for making opaque patterns in calico printing. But its most valuable application is for artificial silk. It is pressed out through fine holes, and the thread resulting quickly solidifies as the solvent evaporates, and can be dried carefully and worked up on reels or bobbins, to be dyed later.
Properties.—Artificial silk, as a rule, is a little stiffer than natural silk, but has an exceedingly fine lustre. It cannot be spun in as fine threads as fine, natural silk, but, on the other hand, can be produced in thick, smooth threads which, stained as a rule black or dark colors, quite replace horsehair for furniture coverings, etc. Similar products are made, too, by coating cotton with a layer of artificial silk.
Another curious use of this artificial silk process is when it is formed into still larger threads, very lustrous and quite stiff, and used for plumes and aigrettes. They can be dyed any color, have excellent lustre, and are extremely useful for millinery.
Precautions Necessary in Dyeing.—One great drawback is common to all these different varieties of artificial silk. They are quite strong, although not particularly elastic, when dry, but when wet lose their strength very markedly. Indeed, at one time it was found extremely troublesome to dye them, as the silk skein dyers, accustomed to work and wring and stretch their silk, with impunity, in and out of the hot dye-baths, would try the same treatment with this new product, and in consequence ruin every skein. When thoroughly wet through in a hot bath the thread will soften until a skein may hardly bear its own weight. Accordingly, the dyeing is always done as quickly as possible, and generally at a lukewarm or only moderately high temperature. The skeins should be handled as little as possible in the dye-bath, and, when taken out to wring, should be rinsed slightly to get rid of extra color, acid, etc., and then carefully dried, not by twisting on two sticks, as is customary with other materials, but by wrapping in cheese cloth or blotting paper and then running the skeins backward and forward through the clothes wringer.
Tests for Artificial Silk.—It has been ascertained that all varieties of artificial silk now on the market are made from some form of cellulose. Efforts have been made to take thick jellies made from gelatine or similar animal compounds, and make threads from them, coagulating them later by treatment with formaldehyde or similar chemicals.
These experiments have, however, not as yet proved successful. Accordingly, any test that will distinguish between a vegetable and an animal fibre will show whether a brilliant thread or piece of textiles contains natural silk or not. The simplest of tests is, of course, to burn a little with a match or at a flame and see if there results the characteristic “burnt feather smell” of charring animal tissues. This odor accompanies the natural silk. The chemist would probably make the same test more accurately by heating a wad of the material in the bottom of a small test tube and noticing whether ammonia was being evolved, and whether the distillate was alkaline in reaction. The ammonia and alkali resulting from the nitrogenous organic matter is a certain indication of animal matter.
To distinguish between mercerized cotton and artificial silk, it is generally enough to soak the samples for a short time, say a quarter of an hour, in boiling water and test their strength. Mercerized cotton properly made would be just as strong afterward as before, while the artificial silk would be soft and weak, if it would not, indeed, break down completely. Besides this, it must be remembered that the mercerized cotton, in spite of its lustre, is made up of threads tightly spun together from a large number of short fibres, none of which are over two inches or so in length, while the artificial silks are made up, like the natural silk, of long, continuous fibres twisted together to form the yarn.