Liquid timers are a calming and mesmerizing device suitable for all ages that also demonstrates some basic scientific principles. Each timer contains coloured fluids of different densities. To create the droplets, the liquids inside the timer must be mutually insoluble. This means that the coloured liquid wont mix with or dissolve into the other coloured liquid or the clear liquid. Because they don’t mix, we can observe gravity at work with the two heavier coloured liquids flowing to the bottom of the timer.