This week, Roy and I decided that we wanted to keep the ball rolling with our new experiments. The days have been mostly grey lately and we really wanted to see a bit of colour. Earlier this week we were looking at Roy's Grandma's kaleidoscope and its swirling, changing colours. I remembered this simple experiment which makes milk swirl with colour, like a kaleidoscope. So this week, for those of you who want a bit of colour in your lives, Roy and I will show you how to make kaleidoscopic milk!
You Will Need:
- Full cream (also known as full fat) milk. Don't try using low fat milk or the experiment won't work.
- Detergent (washing up liquid)
- Liquid food colouring - Roy and I used a couple of drops each of red, blue, green and yellow
- A plate with a rim - you need to put your milk on the plate so make sure it has enough rim that it won't spill.
- 5 teaspoons.
- A bowl (for your dirty spoons)
Method:
- Put a layer of milk onto your plate.
- Pour a little food colouring onto a teaspoon and add about 4 drops to the milk. Repeat this for each colour, but make sure you use a different teaspoon each time. That way, if you have too much you can always tip some back into the bottle! You want to put your food colouring in the centre of the plate, as shown in the photo below!
- Pour a little detergent into your 5th spoon and use this to add a couple of drops of detergent to the very centre of your colour splodges!
- Watch as the milk seems to come to life, pulsing and moving the colours around and (eventually, if you leave it long enough!) merging them together.
What's Happening And Why?
Milk is made up of lots of different things, water, fat, sugar, protein, vitamins and minerals. The water in the milk means that it has a similar surface tension to water. This means that when you drop the food colourings onto the milk they sit there. When you add detergent though, lots of things start to happen. The detergent breaks the bonds which hold the water together so the food colouring can move about. The detergent also change the bonds which suspend the proteins in the milk and they start to move all over the place! On top of that, the soap molecules join together to form what we call micelle. These move the fat around, dispersing it through the milk. This is similar to what happens when you wash the dishes! When the soap and fat are distributed through the milk the movement stops. Normally, the whole process would be invisible but because of the food colouring, we can see everything as it happens!
Now, something for you to explore yourself - what happens if you add more detergent in spots where the colour has pooled when most of the reaction has already finished?