92 WATER 



Steam is the gaseous form of water. Water and ice change to steam 

 at all temperatures. At 100 C. the steam from boiling water has a 

 pressure equal to the pressure of the atmosphere. 



A solution consists of solvent and solute. An emulsion is a mixture 

 in which the suspended substance is so finely divided that it separates 

 itself from the solvent very slowly. 



Solubility of a solid is the weight of it that will dissolve in a definite 

 weight, usually 100 g., of water or other solvent. 



Crystals are solid bodies that take regular shapes when they sep- 

 arate from solution or from the liquid state. Non-crystalline sub- 

 stances are amorphous. 



97. Exercises. 



1. If water were most dense at C., what effect would this fact 

 have upon the depth of ice in winter? 



2. If a test tube of water is placed in a cup of ether, and a rapid 

 current of air is forced through the ether, the water may be frozen. 

 Why? 



3. Which should be kept in the colder room of a storage warehouse, 

 eggs or meat? 



4. The sharp edges of a piece of ice become rounded off even in 

 very cold weather; why? 



5. In making " fudges," or the filling of French candies, why is the 

 candy first cooled without being disturbed, and afterwards stirred 

 rapidly? 



6. Can you dissolve salt in water, and then recover the salt un- 

 changed by boiling off the water? Can you do the same with sugar? 

 Why? 



7. At Quito, in Ecuador, water boils at 90 C., too low for the cook- 

 ing of potatoes; why? Can you suggest how you could make water 

 boil at 100 C. in Quito? 



8. How is salt commonly obtained from salt water? In Northern 

 Russia the salt makers remove much of the water by partly freezing 

 the salt solution, and so save fuel. How is this possible? 



