The science of separation – 1

Avneesh Shukla

If we examine closely, we can find that in our everyday life, we are always separating something or the other. Whether it is the tea we drink by filtering, or water through a filtration system, or separating particulates from the air by wearing a dust mask, separating compounds from the air or water with charcoal, centrifuging the water away from the clothes in a spin cycle of a washing machine, etc. – all these are common examples of separation. In this article I will be sharing my experiences of demonstrating this theme with the students of Government Upper Primary School (Class 6to 8), Uttarakashi.

Before demonstrating this theme, I arranged the following materials and reading resources in the preparatory area:
• Pulses (chana, rajma, urad, etc.)
• Chalk, soil, and sand
• Water and oil
• Salt and sugar
• Beaker and funnel
• Transparent plastic bottle
• Straw
• Naphthalene ball and Cotton
• Glass rod
• Magnets
• Nails
• Sprit and sprit lamp
• Wire gauge and tripod stand
• Simple and what-man filter paper

I divided students into two groups and gave them a mixture of three pulses (chana, rajma, urad, etc.) and asked them to do anything they wanted with the mixture. After thinking and observing for a minute, one group separated the pulses into different sets – chana, rajma, and urad. The second group was not able to do anything. However after observation, the second group too separated the pulses into three sets. Then, I mixed soil and chalk powder and asked the groups to separate them. The two groups separated the bigger sized chalk (calcium carbonate) and some small sized stone particles but they were unable to separate the soil and chalk powder.

After this activity I asked them what they did. They responded saying:
“Since the size of the pulses were different, we were able to separate them, but soil and chalk powder were different. They were mixed together or the size was smaller that’s why we were unable to separate them.”

Then I asked them “what were the criteria by which you separated the pulses in three different sets?”
Their responses were:
“Since these three pulses had different names – Channa, Rajma, and Urad – we could separate them.”

This statement revealed the prior knowledge or understanding of the students about pulses. Then I asked them if the names of these pulses were not known how would the students have separated them? They said they could separate them by using the following criteria:

• Shape and size – The pulses were of different shapes and sizes – rajma has a curved structure similar to the cashew nut, channa has a spherical structure, and urad is smaller and cylindrical in shape.
• Colour – The three pulses also were of different colours – rajma is brown, channa is yellow, and urad is white/creamy in colour.

The size of the pulses made it easy to separate them, but in the case of chalk powder and soil the particle size was smaller and not easy to separate. Then, to connect this activity with their daily life experiences I asked them what they did before cooking rice?
They replied – that before cooking rice, they try to separate the stones that are normally present with the rice grains.

Then I explained that this technique of separation was called hand picking.

Exploring further, I asked them what would be the criteria for separating objects. After thinking for a while, they listed out the criteria: Name, Shape and size, Colour, Smell, Softness and hardness, Viscous and watery, Structure.

In order to connect their activities to the local context I asked if any separation happened during harvesting. After thinking for a while, they responded thus:
• during harvesting we separate stones from the soil by hand picking
• the harvested crop is first threshed with the feet and then the seeds are separated out from stalk
• after threshing, the rice stalks are placed on the ground and beaten with a wooden stick to knock the grains of rice off the stalk
• after this, using a sieve, the mud and the stones are separated.

Since I was aware of rice cultivation practices, I reminded the students about winnowing – removing the rice husk, or outer coverings – which the students had forgotten to list out.

Different separation techniques

Their responses helped me explain to them the different techniques and methods of separation.

• The process or method by which we separate undesirable things or components using our hands is known as hand picking. This method is appropriate if the particle size is bigger. For ex: separation of stone from field, separation of stone particles from rice, etc.
• The process by which the grains are separated from the chaff by hand, or by using the feet, or by animals such as bullocks is known as threshing. The harvested crop is spread on the ground and either donkeys or oxen are made to walk over them until the grains come out of the chaff.
• Separating lighter husk particles from heavier grains of rice is known as winnowing. In this method, the wheat grains containing husk are allowed to fall down from some height while the wind is blowing. The lighter husk particles are carried away by the wind and form a separate heap away from the heavier grains. Thus, the lighter husk particles get separated from the heavier grains.
• The separation of soil or stone particles through a sieve is known as sieving. Sieving is done to separate solid impurities. In this method, the smaller components pass through the sieve and bigger components are left on the sieve.

My session with this class was interesting because I learnt that by demonstrating and highlighting examples from the students’ everyday lives, they felt connected and participated freely in all the discussions. Generally most schools place emphasis on drill and rote learning and too little emphasis on observation, design, analysis, and argumentation and process skills. The aim of science education can be fulfilled only if the science teaching-learning process is governed through a practical approach.

The author is with the Azim Premji Foundation. He can be reached at avneesh.shukla@azimpremjifoundation.org.