198 



ACIDS, ALKALIES, AND CLEANING 



We should have clean bodies for the same reason that we should 

 wear clean clothing, if for no other; viz., in order that the pores of the 

 skin may be permitted to act freely in removing waste, and in evaporat- 

 ing the perspiration. 



The washing of clothing thus has three objects: 



(1) To remove dirt, and to open the pores of the clothing. 



(2) To dry the washed clothing, and to give it a new absorbing 

 surface. 



(3) To destroy the bacteria which are sure to accumulate in the 

 dirt of the skin and clothing. 



224. Soap. To remove dirt we need not only water, 

 but soap. Soap is a salt, or a mixture of salts. The metal 



(cf. 221) present in hard 

 soaps is sodium; in the old- 

 fashioned soft soaps (Fig. 

 195) it was potassium. The 

 acids to which the soaps are 

 related (cf. 221) belong to 

 the class of " fatty" acids, so 

 called because they are ob- 

 tained from the fats. Ex- 

 amples of the natural fats 

 are beef suet, mutton tallow, 

 and lard. Oils are liquid 

 fats. Strictly speaking, we 

 cannot call petroleum products or coal-tar products, 

 such as kerosene or benzene, oils at all. Palm oil, olive 

 oil, and cotton-seed oil are true oils. Soaps are made by 

 the boiling of fats and oils with alkalies. 



When fat is heated with sodium hydroxide, it is " cut," 

 or " saponified." Saponify is from the Latin sapo (soap), 

 and means " to make into soap." As a result of the boil- 



FIG. 195. 



Old Way of Making Soap from Grease 

 and Potash Lye. Negative by T. B. 

 Magath. 



