234 CLOTHING AND ITS USES 



ing an emulsion, and in this condition it is carried off in 

 the water from our hands and substances on which it is 

 placed. The Germans during the late 

 war suffered greatly from the lack of 

 soap. 



Washing powders and their use. - 

 When water is hard or contains mineral 

 substances, such as lime or magnesium, 

 soap cannot well be used. It is less 



An emulsion seen under Wasteful of SOap if SUch Waters are first 

 the microscope. . . 



softened by the addition of washing 

 powders. These usually have washing soda as a base, which 

 combines chemically with the lime in the water, changing it 

 to an insoluble form, so that it does not affect the soap. 

 Washing powders should be dissolved in a tub of water 

 before the clothes are put in. 



Neutralization. Dirt and some stains are removed 

 from materials, as we have seen, by solution and by 

 bleaching. Other stains can be removed by a process 

 known as neutralization. Vinegar and many fruit juices 

 have a sour taste and will turn a piece of blue litmus 

 paper red. A similar color change occurs when blue 

 litmus paper is placed in the presence of any diluted acid, 

 such as nitric or sulphuric. This is a test for acids. Other 

 substances which have a bitter taste and a soapy feeling 

 are called bases. Lye in soap is a strong base, as is soda, 

 also. We find that if bases are tested with red litmus 

 paper, it turns blue. We therefore have an artificial test 

 for acids and bases. If we now add to a solution con- 

 taining a base some acid drop by drop, and keep testing 

 with red litmus paper, we find at length that the com- 

 bination of acid and base does not affect the paper. Neither 



