Traffic lights in a tube

'Traffic light' in a tube - a coloured sugar gradient
Following on from his enjoyment of rainbows on the wall and mixing food colouring, I had an idea of making a rainbow in a tube using a density gradient of coloured sugar solutions. I tried it myself and it was pretty fiddly, and I thought likely to lead to toddler frustration. I still quite liked the idea so simplified it a little and decided to try out making a three-colour gradient with red, orange (amber!) and green to look a little like traffic lights.

He's pretty keen on all things transport related, and has been telling us about traffic lights on every car journey for some time - a little voice pipes up from the back seat to say "red light means stop" when you approach one!  I suggested making traffic lights in a tube, and he was enthusiastic.  So enthusiastic that actually getting out the things we needed without them being experimented with first was a challenge...

We used our lab kit which has some conveniently shaped tubes, but you could use any clear plastic container - for the sugar gradient you're better with something tall and narrow to make the colour separation clearer, but for mixing the solutions first you could use anything.  We also made use of our pipettes, including some new twisty droppers which Learning Resources sent me to try after I had a chat to one of their team about the design of their lab kit.  The twisty droppers are a fun shape but are also longer than the pipette that comes with the kit, so work nicely with the big test tubes.  You could make the sugar gradient by pouring rather than using a pipette/dropper, but you'd need to give a toddler a little more help.

Adding water to sugar

To make our traffic lights, we made three solutions:

1. Red.  This was just water, with red food colouring.

2. Amber.  We mixed 2 teaspoons of sugar with around 50ml of water, and put in a couple of drops of each of red and yellow food colouring.

3. Green.  We mixed 4 teaspoons of sugar with around 50ml of water, and put in a couple of drops of each of yellow and blue food colouring.

We did it in the most labour-intensive way possible, measuring out the sugar into tubes, pipetting water from a beaker into each little tube, adding the food colouring and then mixing, as much of the fun for the small boy is in pipetting and mixing things!

To make the 'traffic lights' we added the green to the big tube.  The green is the one with the most sugar, and therefore the most dense so it stays on the bottom - it's important to add the solutions in order of decreasing sugar/density.  The small boy did this with his twisty dropper, and we used about two thirds of the mix we'd made.  

Next, we did the amber - I tilted the tube for him to add it as slowly as he could down the side of the tube to try and avoid it mixing with the green.  It's fair to say that a toddler's version of squeezing something slowly and carefully isn't quite what you might achieve as an adult, but he tried!  It didn't mix too much, and we then added the red on top the same way.  We made the 'traffic light' that you can see at the top of this blog.  It's not bad, the red and green are clearly at opposite ends, and there is some orange in the middle.  He liked it for about 30 seconds, and then wanted to go and play with something else; the fun was definitely in the making rather than the end result!

Adding the green (most dense) solution to the big tube

I had a go with the remaining solutions (probably about 15ml of each) and a small tube after he'd lost interest, and got a clearer gradient with some slower pipetting.  If you have an older child with a longer attention span and better fine motor skills, you could do a rainbow or other multi-coloured gradient with more than 3 solutions with different amounts of sugar dissolved.  We'll probably come back to this in the future and try another variant, and talk a little more about density as we only discussed having put more sugar in the green than the other colours!  Meanwhile, the 'traffic lights' are still in the tube as it's not mixed during the day (although I did avoid it being shaken!).

Our attempts - the taller one is a good shape and size, but I tried the little one with the leftovers and a steady hand!