mo The Cornell Reading-Courses 



Action of acids on silk. — Silk is readily attacked and disintegrated by 

 a concentrated acid solution. Dilute acid solutions weaken the fabric, 

 but not so seriously as they weaken cotton. 



Action of alkalis on silk. — Concentrated alkali solutions act on silk 

 vigorously, but a little less vigorously than on wool. Dilute alkali solu- 

 tions weaken silk and destroy its luster. 



As laundering concerns itself continually with the action of alkalis and 

 acids on fabrics, the preceding outline should aid one in grasping some of 

 the reasons for the several laundry processes. 



WATER 



A bountiful supply of water good for laundry purposes is an important 

 factor in successful laundering. Water is the natural solvent for much 

 of the dirt that accumulates on clothing; moreover, it acts as a carrier 

 to rid the clothing of all forms of dirt, both soluble and insoluble. Unfor- 

 tunately, good drinking water is not necessarily equally good for laundry 

 purposes, as water may hold in solution substances not hurtful to health 

 but very detrimental to cleaning processes. A water good for the laundry 

 should be clean, soft, clear, odorless, free from discoloration, free from 

 iron, free from organic matter. 



Hard and soft water 



The very characteristic (its solvent power) that renders water valuable 

 as a cleansing agent (detergent) is the cause of its greatest shortcomings; 

 for on its way to us water may pass over, or through, soils that contain 

 soluble substances of an undesirable nature. The characteristic known as 

 hardness, possessed by some waters, is due to the presence of lime salts 

 gathered in the way described. Hard water is not the best for laundry 

 purposes, as lime salts decompose the soap used and form in its place an 

 insoluble lime soap, which collects as a curd on the surface of the water. 

 Such soap decomposition takes place as long as any lime remains in the 

 water and the cleansing (detergent) properties of soap are not in operation 

 until every bit of lime has combined with soap to form lime soap. By 

 leaving minute particles of lime soap in its pores, hard water is said to 

 weaken a fabric. If the available supply of water is hard, then, the prob- 

 lem of the housekeeper is to find some means of removing lime or of reducing 

 its ill effects. 



Temporary and permanent hardness. — According to the nature of the 

 lime salts present, water is said to be either temporarily or permanently 

 hard. Temporary hardness is caused by the presence of carbonate of 

 lime, and such water may be softened by boiling. If the boiled water is 



