DYEING PnocEssF.s. Cotton, silk, and wool are the textile fibres that are usually subjected to processes of dyeing. Uccasif mally the material is dyed before spinning. but usually in the state of yarn or thread. and sometimes as woven cloth. Before dyeing, the fibres are first cleaned so as completely to remove all natural and artificial impurities, such as grease and dirt, which tend to produce spots or uneven shades of color, in consequence of improper fixing of the mordant and color. Whenever light and delicate tints are to be dyed on the fibre, bleaching becomes neces sary. The preliminary steps in the preparation of cotton consists in boiling the fibre in a weak solution of caustic lye. after which it is rinsed and then steeped in a solution of bleaching powder and again rinsed. The third step con sists in steeping it in dilute sulphuric acid, after which it is again cleansed by washing, and dried. Silk is boiled twice in soap in order to remove the natural silk glue which accompanies the crude fibre, and is then bleached by exposure to sulphurous acid fumes produced by burning sulphur. Wool is cleansed by washing and then steeped in soap and sodium carbonate, after which it is well rinsed in water, by means of which the natural grease of the fibre is removed. It is then bleached with sulphur dioxide. The dyeing of mixed cotton and woolen fabrics such a- cashmere and delaines requires special treat ment. and the processes must lie selected so that the colors of the wool and the cotton shall be identical on the finished material. In dyeing with substantive colors, simple immersion of the fibre in a hot dye-bath and carefully working the material beneath the surface, to secure' an even shade, is all that is necessary. The full quantity of the dye is not added at once to the bath. but in successive portions until the desired shade is obtained, the temperature of the bath being gradually raised. The use of mordants has already he•n noted above. In all dyeing
processes. considerable attention must be paid to the permanency of the dyed color, and fast colors are those which withstand the action of air and sunlight. It is obvious that woolen goods and calicoes, which are worn frequently and may be washed, should he dyed with colors that are more fast than those which are used with silks.
Aremf.vrys. The apparatus of the dyer is Pry simple, consisting of vats, kettles, and cis terns, which may be of wood, stone, or metal. In Europe (lie kettles are still heated over open fires, but in America a steam-coil is universally used. A pure water-supply is absolutely. essen tial to successful dyeing. When the available water-supply is einitaminated by sewage or con tains lime, magnesia, or other mineral matter, artificial purification must be employed. Sus pended matter may sometimes be removed by sedimentation or filtration, or the two combined, hut chemical treatment may be required to re move these and other` impurities.
Itumnitat.aeui. The literature of dyeing is very extensive, and reference should be had to the . rticif in the various technical cyclopfedias, as well as to the following works: Crookes, PrtIN its! Handbook of Dyeing and (London. 1574) Hurst, Sill: Dyeing, P rintiny,rent! Pinish i (Glasgow, 159' ; Knecht, Rawson, and Lowenthal. .1 .1/antotl of Dyeing, for the Use of Practical Dycrs, Manu factu•ers, Students. ant! .111 Intercstcd in the .Irt of Dyeing (London. 1893) ; Gardner, it /),tic ing (Philadelphia. 1897): Dgcr and Color ilakcr's Companion (Philadelphia, 1S95) : and Recent Progress in the industries of Dyeing and Colico-l'rinting, being a supplement to Sansone, The Printing of Colton Fabrics I 18951: and. id., Dyeing (Manchester, 1897) ; Sadtler, /m/ustrita Organic Chemistry ( Phila delphia, 1900). See TEXTILE PRINTING; COAL TAR COLORS; MINERAL COLORS; S1oRUA NTS ; and the special articles on the more important dye stuffs.