WOOL AND COTTON DYEING 24$ 



vegetable world was the source of practically all coloring 

 matter, the pulverized root of the madder plant yielding the 

 reds, the leaves and stems of the indigo plant the blues, the 

 heartwood of the tropical logwood tree the blacks and grays, 

 and the fruit of certain palm and locust trees yielding the 

 soft browns. So great was the commercial demand for dye- 

 stuffs that large areas of land were given over to the exclusive 

 cultivation of the more important dye plants. Vegetable dyes 

 are now, however, rarely used because about the year 1856 

 it was discovered that dyes could be obtained from coal tar, 

 the thick sticky liquid formed as a by-product in the manu- 

 facture of coal gas. These artificial coal-jtar, or aniline, dyes 

 have practically undisputed sway to-day, and the vast areas 

 of land formerly used for the cultivation of vegetable dyes 

 are now free for other purposes. 



226. Wool and Cotton Dyeing. If a piece of wool is soaked 

 in a solution of a coal-tar dye, such as magenta, the fiber 

 of the cloth draws some of the dye out of the solution and 

 absorbs it, becoming in consequence beautifully colored. The 

 coloring matter becomes " part and parcel," as it were, of 

 the wool fiber, because repeated washing of the fabric fails to 

 remove the newly acquired color ; the magenta coloring matter 

 unites chemically with the fiber of the wool, and forms with 

 it a compound insoluble in water, and hence fast to washing. 



But if cotton is used instead of wool, the acquired color is 

 very faint, and washes off readily. This is because cotton 

 fibers possess no chemical substance capable of uniting with 

 the coloring matter to form a compound insoluble in water. 



If magenta is replaced by other artificial dyes, for example, 

 scarlets, the result is similar; in general, wool material ab- 

 sorbs dye readily, and uniting with it is permanently dyed. 

 Cotton material, on the other hand, does not combine chemically 

 with coloring matter and therefore is only faintly tinged with 



