With back-to-school barrelling toward us, this week’s Let’s Discover! experiment is one that often finds its way into elementary classrooms. It is colourful, fun, and has a built-in lesson on the science of keeping clean. All you will need is milk, liquid soap, food colouring, a plate (or bowl, or a pan) and a cotton swab.
The “milky fireworks” experiment, as it is commonly known, is simple to set up: get a shallow, broad container (like a plate), pour some milk into it and place some dots of food colouring into its centre. The milk is pretty thick, so the colour will stay where you put it. Now take a cotton swab, dip it in soap (or drop some soap onto it) and press the swab’s tip into the plate where you placed the dye. The results should be spectacular! The colour will very quickly migrate away from the centre of the plate, giving a lovely pattern. Each time you press the swab against the plate, it should have a similar effect.
The scientific part of this experiment is how the soap and the milk interact with one another. Milk is mostly water, but it contains plenty of fats and oils that float in little bubbles within the milk – this is what makes milk products thick. Soap breaks up these bubbles of oil, letting them flow more freely and mix with the water, which lets the food dye flow, too. This is why we use soap to clean dirt off of us: it makes things much easier to dissolve in water, so soap and water work together to clean our skin. It also explains why soap can dry skin out: we need a little of our natural skin oils, or our skin becomes dry.
This experiment also works with black pepper floating on water – less colourful, but still fun!
We are all about water at Discovery Centre, this year! Our brand-new exhibit, TANKED: An Atlantic Aquarium Exhibit, has loads of Nova Scotia fish, a giant lobster and touch tanks full of fascinating sea creatures. Wednesday evenings, we’re open until 8:00, and our touch tanks are often open all evening!