MATERIALS OF CLOTHING 201 



the lime soap gets into the pores of the fabric, and in- 

 jures it. 



If a soft water cannot be obtained in any other way, a method of 

 " softening " should be used. To remove permanent hardness from a 

 laundry water we often use soda or borax. Borax is sodium borate. 



Sodium carbonate (or borate) -f calcium sulphate give 

 (soluble) (soluble) 



sodium sulphate + calcium carbonate (or borate). 



(soluble) (insoluble) 



The sodium sulphate left in the solution has no action with the soap. 

 Both temporary and permanent hardness may be removed at one opera- 

 tion by the correct amount of ammonia water or caustic soda. 



Washing powders also precipitate hardness. They are usually soda 

 or potash, or dried soap containing an excess of alkali. 



227. Materials of Clothing. Two common vegetable 

 fibers used for clothing and in the household are cotton 

 and linen. Cotton is the covering of the seed of the cotton 

 plant; while linen is found in the stalks of flax. Both are 

 chiefly cellulose (cf. 123). 



Although cotton and linen are much alike chemically, 

 they are very different physically. Both consist of hollow 

 tubes (Fig. 197); but the fibers of cotton are flat and 

 twisted, while those of linen are nearly straight, and have 

 thick walls with a central opening. 

 Linen cloth r is stronger than cotton, 

 but cotton is lighter and more elastic. 



Cotton and linen are easily de- 

 stroyed by mineral acids (cf. 214), 

 if these are strong or are allowed to FlG- 197 ' 



dry upon the fabric. They are not 



Wool 

 L97. 

 Fibers of Cotton, Linen, 



