SOLUTIONS OF A SOLID IX A LIQUID 9 



Increase in pressure of a gas above a liquid increases the solubility, i.e. 

 the concentration of that gas in the liquid. For sparingly soluble gases the 

 increase in solubility is directly proportional to the increase in pressure ("Law 

 of Henry"). This principle also holds qualitatively, but not quantitatively, 

 for the very soluble gases. 



When a mixture of several gases is maintained over water, each dissolves 

 independently and in accordance with the gaseous pressure ("partial pressure") 

 which it exerts against the surface of the water ("Law of Dalton"). This 

 principle holds strictly only for those gases which are slightly soluble in water. 

 For example about one-fifth of the atmospheric pressure is due to the oxygen 

 present. Assuming an atmospheric pressure of 760 mm. Hg (the value at 

 standard conditions), the pressure due to the oxygen is equivalent to about 

 152 mm. Hg. The quantity of oxygen which dissolves in water exposed to 

 the air is the same as that which would dissolve if oxygen only at a pressure 

 of 152 mm. Hg occupied the space over the water. 



Solutions of a Liquid in a Liquid. — In general solutions of a liquid 

 in a liquid fall into two classes : those in which the liquids are freely miscible 

 with each other in all proportions, and those in which each liquid reaches a 

 definite point of saturation in the other. Alcohol and water, for example, mix 

 with each other in all proportions; such a solution is an example of the first 

 mentioned type. Many oily liquids also are miscible with each other in all 

 proportions. A familiar example is the solution of lubricating oil in gasoline. 

 In solutions of this kind the liquid present in excess is usually considered to be 

 the solvent. In a 50 per cent solution of alcohol and water, either liquid 

 could be considered the solvent, or either could be considered the solute. 



Ether, chloroform, and many other liquids are sparingly soluble in water. 

 After water and ether, for example, are shaken together in a flask, two dis- 

 tinct layers of liquid separate upon standing. The upper layer consists of the 

 lighter ether, saturated with water, while the lower consists of water saturated 

 with ether. In both layers, however, the concentration of solute present at 

 saturation is small. In the upper laj'er ether is the solvent, water the solute ; 

 the converse is true of the lower layer. 



Solutions of a Solid in a Liquid. — This is by far the most familiar 

 type of solution and in many respects the most important. Substances in the 

 solid state vary greatly in their solubility in water, ranging all the way from 

 those which are virtually insoluble to those which are extremely soluble. There 

 is usually a limit to the amount of any solute which can be dissolved in a given 

 volume of water at a given temperature. When this limiting concentration is 

 reached the solution is said to be saturated, following the same terminology 

 used with solutions of gases and liquids in liquids. It is almost impossible to 



