SOLUTIONS 135 



be mentioned here. Emulsions may be defined as two sub- 

 stances that will not mix without the addition of a third. One 

 of the substances is usually a fat or an oil. The kerosene 

 emulsion frequently used to kill insects on plants is made of 

 kerosene and water to which is added a quantity of soap. 

 Kerosene and water will not mix, but the soap causes them to 

 form an emulsion. The ingredients in emulsions are likely to 

 separate out if left standing for some time, but readily mix 

 again when well shaken. 



Practical Exercises 



1. Put a small quantity of clay in one test-tube and a crystal of potas- 

 sium permanganate in another. Fill each half full of water and shake 

 thoroughly. In which tube is the matter suspended and in which 

 dissolved? 



2. Is a solution necessarily colorless? 



3. How do you explain the fact that some substances, which will 

 not dissolve in a cold liquid, will dissolve when the liquid is heated? 



4. When streams are muddy after a rain, is the material dissolved or 

 suspended in the water? 



5. Why is the sea salt, if all the rivers that run into it appear to be 

 fresh? 



6. Explain how water may form caves. 



7. In caves, stalactites (long points of stone, like icicles) are often 

 formed by water containing mineral matter which seeps through the 

 roof. Explain how the water evaporating may form these objects. 



8. Which do you consider the better bluing for laundry purposes, one 

 that is dissolved in the water or one that is suspended in it? 



