_Dyeing of Mercerized Cotton._—Cotton, thus treated, is dyed in the same way that ordinary cotton is, with the exception that it takes the dyes more rapidly, and, as a rule, gives deeper and more brilliant shades with the same amount of coloring matter. For special purposes it may be best to use the Sulphur or the Vat dyes, but in general this material is best dyed with the Salt dyes, which are not only easy to apply, but are fast to light, very brilliant, and on these goods, at any rate, very fairly fast to washing. As before mentioned, the fastness to both light and washing may be considerably improved by after treatment of the dyed goods, i.e., by passing them through a hot bath containing a tablespoonful each of copper sulphate, potassium bichromate, and acetic acid to the gallon of water. This, however, will rarely be found necessary, provided the selected colors are used, and the color has been applied at the boil in a bath containing considerable salt. ARTIFICIAL SILK =History.=—The famous old French chemist, Réaumur, in the year 1734, suggested, after a study of the silk worm, and of the method by which it “spins” the natural thread, that it might be possible to make a jelly-like substance which could be drawn out into a fine thread and, coagulating, form an artificial silk. This suggestion was first acted on, in a practical way, in the year 1855, when Andermars obtained some curious results by dipping a needle or fine metal rod into a thin viscous solution known as collodion, and then drawing it out rapidly, made fine, smooth threads as the material solidified. This collodion, which for many years has been in common use in minor surgery to paint on wounds and cuts, because it leaves a film of artificial skin, and in more recent times has been much used in photography, is a solution of gun cotton or nitro-cellulose in a mixture of alcohol and ether. In 1885 Count Hilary de Chardonnet made improvements in this last process, and produced successfully the first real artificial silk threads on a commercial scale. _Chardonnet Silk._—He also used a thick collodion solution, but instead of _drawing_ it out he _pressed_ it out through fine holes by using very great pressure. As fast as the gummy thread exuded it was picked up, carried along into a drying room, where the alcohol and ether could escape (to be condensed later and used over again), and then the solid fibre was passed into a solution of some suitable reducing agent, such as ammonium or sodium sulphydrate, which converts the inflammable gun cotton into its original condition of cellulose. These resulting threads, being smooth and uniform when properly made, have very great lustre. Indeed, they are often far more brilliant than the very best and finest natural silk, and can be dyed and woven into beautiful fabrics.