14 CRYSTALS a Crystal growth Sodium thiosulphate crystals grow rapidly from a supersaturated aqueous solution The formula for the crystals is Na2S2O310H2O On heating these crystals dissolve in some of their water of crystallization Put 3 cm of sodium thiosulphate crystals in a testtube Add 2 drops of water Heat gently until all the crystals have dissolved They appear to melt Leave to cool Crystals may not form unless you drop a tiny seed crystal of sodium thiosulphate into the solution Then crystal growth commences and spreads rapidly through the whole solution Watch the growth from one centre Hold the tube in the hand while crystallization occurs