Heating copper sulphate solution over boiling water. Heating over boiling water ensures that the temperature of the solution does not exceed its own boiling point, which would happen if the solution was heated directly. As the temperature of the solution rises, more and more solid copper sulphate can be dissolved in it, up to a point known as the saturation point. As the solution cools, copper sulphate crystals will form in it, as the cool solution cannot hold as much copper sulphate as it could when it was warmer.