This week we had great fun conducting an experiment to construct lava lamps in class. We discussed the concepts of density and solubility and made lots of predictions before our experiment. We carefully observed our experiment and were able to analyse what had happened. When you drop the an effervescent tablet into the oil and water, it falls down through the oil (it does not dissolve in the oil) to the bottom, where it reacts with the water (a chemical reaction) to produce carbon dioxide gas. These bubbles of gas rise through the oil to the top of the bottle because they are light, taking some coloured water with them. The bubbles of gas burst when they reach the top, the gas escapes, and the drops of coloured water sink back down through the oil.