sand is a kind of solid & clay is a kind of solid ->  a mixture of clay and sand is a kind of solid mixture  a mixture of clay and sand is a kind of solid mixture & sand particles are bigger in size than clay particles ->  sand and clay is a solid mixture of different sized particles  sand and clay is a solid mixture of different sized particles & a sifter can be used for separating a mixture of different sized solids -> a sifter can be used to separate sand and clay in the soil