Using milk, food colouring and washing-up liquid, 4th and 5th class carried out a scientific investigation to explore the presence of molecules in a liquid. First, milk was poured into a plate. Next, drops of food colouring were added. The food colouring was used so that the reaction and movement in the liquid could be seen. Lastly, washing-up liquid on a cotton bud was placed on the surface of the milk. The class observed and noted the result. The soap broke the surface-tension of the milk which caused the colours to disperse. The mixing of the milk and soap caused the molecules in the liquid to separate, creating the movement of the colours!