CHAPTER XL 

 SYNTHETIC ORGANIC PRODUCTS 



MENTION was made several times in the preceding chapter of 

 the use of salts of aluminium in dyeing. A brief summary of the 

 chemistry of dyeing and dyestuffs is all that can be presented 

 here. A still more restricted resume of some other important 

 synthetic organic products is also given. The products included 

 are, on the constructive side, perfumes, drugs and plastics (includ- 

 ing rubber) ; on the destructive side, explosives and toxic gases. 



Some dyes, perfumes and drugs are still, of course, obtained 

 from natural sources, and synthetic rubber continues to show 

 but little promise of superseding plantation rubber in the near 

 future. Nevertheless, the interest of the chemist in the fields 

 here under discussion is almost entirely synthetic, seeking to 

 duplicate natural products by laboratory methods and to dis- 

 cover new products of even greater use to humanity. 



Dyeing. The problem of the dyer is to confer the desired 

 color upon a fabric made, usually, of cotton, linen, wool, or silk, 

 and to do this in such a way that the dye is fast to (i.e., is not 

 removed or destroyed by) rubbing and light, and often, also, 

 to washing with soap. To understand the means by which this 

 is achieved, it must be noted that cotton and linen consist of 

 smooth hollow fibers (Fig. 2, p. 2) of cellulose. Wool is made 

 of hollow fibers with a scaley surface, and silk of solid filaments, 

 but these are composed of proteins (p. 438). Now, the proteins 

 are much more active chemically than is cellulose, and also, as 

 colloidal materials, seem to have a much greater tendency to 

 adsorb other substances (see pp. 422, 443) than has cellulose. 

 Hence, accidental stains on wool or silk are much less often remov- 



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