EMULSIONS 145 



aside and allow it to stand for a short time. Does the oil remain 

 mixed with the water? 



Put oil and water into another test tube and add finely shaved 

 soap or a little soap solution Shake the test tube vigorously and 

 set it aside for a while. Does the oil now rise to the surface ? 



When the oil was shaken with the water, it divided into 

 minute globules scattered through the water, giving the 

 mixture a milky appearance. The oil soon separated from the 

 water and floated on top of the water just as it did before 

 the test tube was shaken. When soap was added and 

 shaken with the oil and water, the globules remained in 

 suspension and did not separate from the water when it 

 was set aside for a while. A suspension of this kind is 

 called an emulsion. 



It is the power of emulsifying oil and grease that makes 

 soap so useful as a cleansing agent. Water will not dis- 

 solve grease; but when soap solution is rubbed on oily or 

 greasy materials, the oil or grease is converted into little 

 droplets, each surrounded by a film of soap solution. These, 

 with the little particles of dust and dirt which they contain, 

 are easily removed by rinsing with water. The natural 

 oils of the skin accumulate impurities from various sources. 

 Since water will not dissolve this oil, soap is an essential in 

 bathing. 



If soap is used in hard water, a sticky white substance is 

 formed which will not dissolve in water. This gummy 

 substance is a chemical combination of soap with the mineral 

 salts dissolved in the water. The soap combines chemically 

 with these mineral salts until all the salts are broken up and 

 the water is softened. Until enough soap is dissolved to 

 soften the water, an emulsion will not form. This results in 

 such a great waste of soap that cheaper substances such 



