88 WATER 



amount of potassium permanganate, or of aniline viokt, 

 shows a remarkable power of coloring water. But 

 whether colorless or colored, true solutions are clear, not 

 roily (cf. 84). 



Milk is a mixture of water, sugar, etc., with suspended particles of 

 fat. The fat is very finely divided, and the casein of the milk (cf. 

 357) prevents the water and fat from separating at once into two 

 distinct layers. After a while, however, the |fat (cream) rises to the 

 top. A mixture like milk is called an emulsion. 



92. Properties of Solutions. A solute not only im- 

 parts its taste and color to a solution, but it makes the 

 boiling point, freezing point, and density of the solution 

 differ from those of the solvent. A solution of a solid 

 boils at a higher temperature, and freezes at a lower 

 temperature, than the pure solvent. Thus, a solution of 

 40 g. of salt in 100 g. of water boils at about 108 C. A 

 saturated salt brine does not freeze until the temperature 

 is about 22 C. Because of its dissolved solids, ocean 

 water rarely freezes in temperate latitudes. 



When a dilute salt brine freezes partly, but not wholly, 

 most of the salt remains in the solution, and the ice is 

 nearly fresh. 



A solution of a solid has a greater density than the 

 solvent. Thus, while a liter of pure water weighs about 

 1000 g., the same volume of sea water weighs about 1026 

 g. (cf. 80). 



93. Freezing Mixtures. When most solids dissolve 

 in water, they lower the temperature of the water. Thus, 

 if equal parts, by weight, of ammonium nitrate and water 

 are mixed at C., the temperature falls to 15 C. 



