110 SMITH'S INTERMEDIATE CHEMISTRY 



stand they slowly rise to the top, being lighter than the water 

 in which they are not dissolved, but suspended. A mixture of two 

 liquids of this nature is called an emulsion. 



Chemists commonly call the dissolved substance the solute and 

 the substance in which it is dissolved the solvent. In many cases, 

 however, (when we take two liquids such as alcohol and water, 

 for example) the terms solvent and solute are interchangeable. 

 Gases, liquids, and solids may all be solutes, and dissolve in 

 suitable gaseous, liquid, or solid solvents. 



Solvents. Water is by far the commonest and most useful 

 solvent. Very many inorganic substances dissolve in it easily. 

 The fact that many (like sulphur and sand) do not, enables us to 

 separate the components of a mixture containing a soluble and an 

 insoluble substance. 



Many organic substances, such as fats, paraffin, petroleum, tar, 

 rubber, cotton, paper, shellac, and so forth, do not dissolve to any 

 measurable extent in water. But fats dissolve readily in ether 

 (C 4 Hi O), in carbon disulphide (CS 2 ), in carbon tetrachloride 

 (CC1 4 ), and in chloroform (CHC1 3 ). For this reason these sub- 

 stances remove grease which has accidentally got into cloth. 

 Paraffin, petroleum, and tar dissolve in gasoline (petrol), and in 

 benzene (C<jH 6 ). Cotton and pure paper (like filter paper) will 

 dissolve in strong sulphuric acid. Alcohol (C 2 H 6 0) dissolves 

 shellac (to make varnish). 



Again, water dissolves little carbon disulphide, chloroform, 

 carbon tetrachloride, gasoline or benzene. But it dissolves alcohol 

 in any amount, and ether in limited quantity. Some organic 

 substances, like sugar, dissolve easily in water, but hardly at all 

 in the other solvents just mentioned. Hence candy or molasses 

 can be taken out of cloth by water, but not by solvents for 

 fats. 



Saturation. As a rule, not more than a certain amount 

 of a solute is dissolved by a given quantity of the solvent. By 



