DYEING 71 



a. Soak a piece of new, white cotton cloth for 5 minutes in a 

 10 per cent solution of sodium hydroxide. Then take out the 

 cotton, wash it free from the alkali, and dry it. Has the cotton 

 been changed in any way? Treat a piece of white cotton 

 thread in the same way; is the thread noticeably weaker, or 

 not? What is the mercerizing process? See 227, text. 



6. Test the strength required to break a piece of white 

 woolen yarn. Now soak it for 5 minutes in a 10 per cent 

 sodium hydroxide solution, rinse out the alkali, and again test 

 the strength of the yarn. Result? Do you think that a 

 "strong" soap, that is, one containing much alkali, would be 

 good for woolens? 



c. Soak a piece of white cotton cloth in dilute sulphuric acid 

 for 5 minutes. Dry it without rinsing; then rub it between 

 your hands. What becomes of it? Do the same to a piece of 

 white wool (flannel or yarn). Is it affected like the cotton? 



d. Get a piece of mixed cloth, that is, one consisting of both 

 cotton and wool. Soak it in dilute sulphuric acid, and dry it 

 without rinsing. Rub it between the hands; what falls out? 

 Which material is this? 



e. Take another piece of the mixed cloth, and boil it for 

 5 minutes (Care ! Do not let the alkali spatter into your eyes !) 

 in a beaker or "tin" can with 10 cu. cm. of 10 per cent sodium 

 hydroxide. This takes out the wool. What happens to the 

 cloth's appearance? Rinse out the alkali, and dry the cotton. 

 If you wished to get the exact proportion, by weight, of cotton 

 and wool in a cloth, how would you proceed? 



EXERCISE 69 

 DYEING 



Apparatus and Materials. Bottle or flask; beakers or dishes of 

 porcelain or enameled ware; solutions of alum, lead acetate ("sugar of 



