Why does the milkiness disappear when CO2 is added in lime water for a long time?

When you first start to bubble carbon dioxide through limewater (calcium hydroxide solution), they react and form calcium carbonate. This isn't very soluble, so you see it as a mist of fine particles of chalk, which we describe as 'the limewater has gone cloudy/ milky'. As you continue to bubble, carbon dioxide dissolves in the water to form carbonic acid, which dissolves the calcium carbonate, so the milkiness disappears. Here are the reactions: Ca(OH)2 + CO2 --> CaCO3 + H2O forming the milkiness 2H2CO3 + CaCO3 --> Ca(HCO3)2 + H2O +CO2 removing the milkiness again This second reaction is the same one as for rainwater flowing over limestone rocks.