i8 



GENERAL SCIENCE 



this oil is not removed from the skin and so the water 

 cannot remove the dirt. To understand how the soap 

 removes this oil it will be necessary to know what an 

 emulsion is and how it is made. 



When little particles of fat are broken up so finely 

 that they seem to mix and disappear in water, this mix- 

 ture of particles of fat and water is called an. emulsion. 

 Milk is a typical ex- 

 ample of a good emul- 

 sion in which the fat 

 globules rise to the 

 surface as cream, if it 

 is allowed to stand 

 for several hours. An 

 emulsion can be made 



GLOBULES O F FAT IN MILK 

 A good type of an emulsion. (Magnified.) 



by taking some oil and 



shaking it with some base in a test tube. The base 

 breaks up the oil into fine globules so that they mix 

 with the solution easily. 



Since all soaps are slightly basic, the base acts on the 

 oil or grease on the hands and face and forms an emulsion 

 which mixes with the wash water and then the water easily 

 takes the dirt away also. The same is true of the re- 

 moval of dirt from clothing, except that usually a soap 

 is used having a greater excess of base, which forms an 

 emulsion of the grease in the clothing and sets the dirt 

 free. 



Nearly everyone is familiar with the fact that soap 

 does not work well in all kinds of water. In some water 

 soap will easily form an emulsion of fat and also a good 

 lather or soap foam. This water is said to be "soft" 

 water, and it does not contain any chemical that will 

 act on soap and prevent the formation of an emulsion. 



