Many of the procedures developed by alchemists and early chemists for the preparation of pure substances, such as distillation and recrystallization, were methods of separating the component substances of naturally occurring solutions. Solutions may be solids, liquids, or gases. Bronze and brass are solid solutions of metals in each other, usually called alloys . The fillings of teeth are liquid or solid solutions of gold or silver in mercury which are called amalgams . The air we breathe is a more or less homogeneous solution of gases in each other.
Sea water is a more or less homogeneous solution of salts in water.
Most of the solutions encountered in nature are solutions which are liquid, at least at the temperatures and pressures at which we will study them. The component or components present in largest quantity in such solutions is called the solvent, and in liquid solutions the pure solvent component is almost always a liquid. The other components are called solutes. Solutes are said to dissolve in the solvent to form the solution. Chemical reactions often take place in solutions.