WATER AS A SOLVENT 139 



tubs of water to keep their cellars above the freezing point. 

 For the same reason orange groves are often irrigated when 

 a heavy frost threatens. 



This capacity for holding heat makes bodies of water warm 

 up slowly in the summer and cool off slowly as winter 

 approaches. If we bear in mind that practically the 

 entire mass of a body of water must reach a uniform tem- 

 perature of 4 C. before it begins to freeze at the surface, 

 this slowness of water to change temperature will explain 

 why large bodies of water so seldom freeze except 

 around the shallow edges. 



Water as a Solvent. Experiment 59. Put a 

 little salt into water in a clean beaker or drinking glass, 

 and stir. The solid entirely disappears. Taste the 

 water. Has the salt affected the water in any way? 

 Pour out three fourths of the water and taste again. 

 Is there any difference between the saltiness of the 

 upper portion and the lower portion of the water? 



Experiment 60. (Teacher's Experiment.) Fill a 

 tall bottle with water colored with blue litmus. By JP IQURE 73 

 means of a long thistle tube, slowly pour a little 

 sulphuric acid into the bottom of the bottle. (Figure 73.) Allow 

 the bottle to stand undisturbed and note the gradual change in 

 color of the litmus, showing that the heavier acid is mixing, or 

 diffusing, upward through the water. 



Experiments 59 and 60 show that when substances are 

 dissolved in water they tend to mix thoroughly with the 

 water and to form a uniform solution. When we mix 

 water, lemon juice, and sugar together to make lemonade, 

 the solution has a uniform taste throughout. Neither the 

 solid nor the liquid tend to separate out of the solution 

 nor to accumulate in any one part of it. As a result 

 of this characteristic of solutions, the water of the whole 



