SOME CHEMISTRY OF EVERYDAY LIFE 177 



Metabolism has reference to those chemical changes occurring in 

 the body concerned with its nourishment, and with the removal from 

 its cells of all waste material. 



THE CHEMISTRY OF CLEANING 



No matter how thoroughly oil and water may be shaken 

 together they soon separate. There is less of adhesive force 

 between oil and water than of cohesion between water and 

 water, or between oil and oil. If, however, there be shaken 

 up with them some such substance as the white of egg (albu- 

 men), it is possible to cause the oil to remain mixed with the 

 water. A liquid mixture containing suspended (not dis- 

 solved) oil or fat particles is called an emulsion. It generally 

 has a milk-like appearance. 



The value of soap as a cleansing agent depends in part 

 upon the fact that when dissolved in water it serves to form 

 an emulsion with oily or greasy matter. The use of soap is 

 commonly accompanied by chemical changes of importance, 

 too, especially in the case of laundry soaps. 



Gasoline when applied to a grease spot on clothing simply 

 dissolves the grease, and the cloth may then be freed of the 

 grease by a thorough rinsing. If a strip of absorbent cloth 

 is put underneath, and gasoline is applied to the spot, any 

 washing of the garment may be unnecessary. The garment 

 can be dried with a hot flat-iron, using a blotter or other 

 absorbent body under the place where the spot was. 



If a strong ammonia solution be applied to a grease spot a 

 chemical union occurs, and the new substance formed is 

 soluble in water and may be washed out. If, however, the 

 cloth is allowed to dry without a thorough rinsing, the new 

 compound (which is of the nature of a soap) undergoes 

 change, and the grease spot reappears in the cloth much 

 enlarged by capillary action. 



If instead of ammonia water a laundry soap is used, a 

 similar chemical change occurs between the grease and a 



