Separation of Substances Notes

• Threshing is usually done in the field, near the field or at the nearest road.
• Usually, a machine thresher works with a drum as axial.
• The crop turns around an axial.
• The drums have “teeth” on the surface.
• The teeth of the drum separates the grains from the straw by beating it.

Cleaning:

• Cleaning is one of the last methods of harvesting process.
• Cleaning grain means removing all the materials other than grain.

Importance:

1. The quantity of the mixture is small.
2. The unwanted substance is present in smaller quantities and the size, shape, or colour of the unwanted substance is different from that of the useful one.

Sieving:

• It is a simple and convenient method of separating particles of different sizes.

e.g.: A small sieve is used for sifting flour.

It has small holes which allow only very fine flour particles to pass through.

• The process of separating insoluble solids suspended in a liquid by allowing them to settle down is called sedimentation.

• Mud settles down when muddy water is kept for a long time.
• Tiny pieces of straw, leaves and other lighter impurities float at the surface of the muddy water.
• The water, which contains these impurities, is then poured out and discarded.