iio8 The Cornell Reading-Courses 



The organic acids — such as acetic axid in vinegar, oxalic acid in 

 tomatoes, tartaric acid in grapes, and citric acid in lemons — have no 

 action on cotton and linen unless they are allowed to dry on the fabric 

 and are subsequently moistened and ironed dry with a hot iron. Then 

 destructive results are produced. 



The presence of starch in the cloth lessens the destructive action of any 

 of the acids on it. 



Action of alkalis on cotton and linen. — The action of alkalis on cellulose 

 differs from that of acids. Dilute washing-soda solution, borax, and soap 

 have little or no harmful action on cotton or linen, but lye is more destruc- 

 tive to these fabrics, especially at high temperatures and if allowed to 

 act for any length of time in the presence of air. If a fabric made from 

 cotton fibers is immersed for two minutes in a strong solution of lye it 

 assumes a gelatinous appearance, and if it is then immediately removed' 

 and washed free of the lye it is found to have shrunken greatly and to have 

 become much closer and firmer in texture than it was before the immersion. 

 The action of the strong alkali for the limited time mentioned has actually 

 strengthened the cloth. It was thought at one time that the process just 

 described would be very valuable in the manufacture of textile goods, 

 but it so increased the strength of the fabric treated that garments were 

 slow to wear out; hence its use was discontinued because it lessened sales 

 for the manufacturer. A modification of the process, known as mercer- 

 ization, gives to cotton goods a glossy, silky appearance without 

 materially increasing its durability. It must not be thought, however, 

 that because the limited action of strong alkali strengthens a fabric, its 

 long-continued action will be harmless. Its first effect is strengthening, 

 but if its action is continued beyond the brief time mentioned it will gradu- 

 ally destroy cloth. 



Wool 



Many animals have a hairy covering, called wool. Wool is the most 

 important animal fiber used in the manufacture of clothing. When 

 woolen cloth is washed it undergoes a characteristic shrinkage. This 



shrinkage is increased by the use 



of strong soaps, by rubbing, by 



quick changes in temperature 



Pfft Ik] II K l©4 M it ^^^^^ ^^® iohvic is wet, by the use 



^i§$ Wn h i W^ P fe of strong alkaHs, or by ironing 



^ ^^ M % n im m M with hot irons. 



Wool fiber has a characteristic 

 Fig. 40. — Woolen fibers , j-i u 



appearance and may readily be 



distinguished under the microscope from any other textile fiber. 



Its surface is covered with little horny scales, all laid in one direction. 



