_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.