Azeotropes (constant boiling liquid mixtures) :

The solution which show positive deviation from Raoult's law, at one of the intermediate compositions have total high vapour pressure or low boiling point. On the otherhand, the solutions showing negative deviations from Raoult's law, for one instermediate compositions, shows lowest vapour pressure highest boiling point. For liquid pairs of such intermediate compositions, the compositions of both liquid and vapour phases is the sane. As a result, both the components present in the liquid mixture will boil at the same temperature without undergoing any change in composition.

        This type of liquid mixture which boils at the same temperature without undergoing any change in composition is known as constant boiling mixture or azeotropic mixture or azeotroes. 

Azeotropic liquid mixtures present in binary solution are of two type: 

(I) Minimum boiling azeotropes: 

These are formed in case binary liquid mixtures showing positive deviation form Raoult's law. For example, a liquid mixture 95.57 mass percent of ethyl alcohol and 4.43 mass percent of water represents a constant boiling azeotropes. This mixture boils at 351.1K which is less than the boiling point of both ethyl alcohol (351.3 K) and water (373 k). This is known as minimum boiling azeotrope because the partial vapour pressure of both the components are maximum. At it's boiling point, both water and ethyl alcohol distill over as if they are the constituents of pure liquid.

Maximum boiling azeotropes:

These are formed in case of binary liquid mixtures showing negative deviations from Raoult's law. Such azeotroes have boiling point higher than either of its pure components. For example , mixture containing 68% nitric acid (boiling point 359 K) and 32% water (boiling point 3.73 K) from a constant boiling azeotrope having boiling point 393.5 K.