In our day to day life we might have separate the useful substance from the mixture.  
For example rice and pulses are cleaned before they cooked. We find tiny stones, small insects and husk among the grains. We need to separate them before they are cooked.

Substances are mostly available in 
mixtures. A few substances are available in pure form. Hence, we need to separate the useful substance from the mixture by using some methods.
Before studying the various 
separation methods we should know the need to separate the components of a mixture.

Need for separation of substances
Substances need to be separated from each other to remove impurities or to get two or more useful products.

Separation of substances can be carried out under two conditions
     •  Dry conditions
     •  Wet conditions

Separation of substances under dry conditions
There are various methods for separating substances, such as handpicking, threshing, winnowing and sieving.

It involves simply picking out substances by hand and separating them from others. The substances being separated may be impurities that have to be thrown away or it may be that both the substances being separated are useful – such as if you separate green grapes from black ones from a 
mixture of the two. But it is very hard to use for bigger quantity and would take time.