Coloured Milk Pump

Psychedelic rules!

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Purpose -

A great introduction to the effect of detergent on surface tension

Nature - 

Demonstration

Materials - 

a glass bowl, milk, food colours, a dropper of detergent

Method - 

· Half fill the bowl with milk.

· Place three or four different coloured drops of food colouring evenly spaced on the milk surface.

· Onto the centre of each food colour spot drip a spot detergent and watch the colours swirl.

· If you watch carefully at the edge of the bowl you can see that the colours slide down the side of the bowl as well as across the milk surface. 

Safety -

Nil.

Explanation -

The milk molecules are pulling against each other tightly to form surface tension.  Detergent breaks these bonds causing a recoil effect away from the detergent drop.  The food colouring is simply there to help us see the molecular action. 

Notes -

Of course this ability of detergent to break the bond between fats is what makes it useful in cleaning dishes, clothes etc.  

This can be done as a class practical by giving each group a Petri dish, a droppers of food colouring, a dropper of detergent and some milk.