Effect of Carbon Dioxide on Lime Water
When carbon dioxide gas is bubbled through lime water, it reacts with the calcium hydroxide present in the lime water to form calcium carbonate. The reaction can be represented as follows:
CO2(g) + Ca(OH)2(aq) → CaCO3(s) + H2O(l)

Small Amount of Carbon Dioxide
When a small amount of carbon dioxide is bubbled through lime water, the lime water turns milky due to the formation of a white precipitate of calcium carbonate. This indicates the presence of carbon dioxide in the gas being bubbled through the lime water.

Excess Carbon Dioxide
When an excess amount of carbon dioxide is bubbled through lime water, the milky appearance disappears. This is because the calcium carbonate formed initially reacts further with the excess carbon dioxide to form calcium bicarbonate, which is soluble in water. The reaction can be represented as:
CaCO3(s) + CO2(g) + H2O(l) → Ca(HCO3)2(aq)
As a result, the solution becomes clear again, indicating the formation of calcium bicarbonate. This reaction is the basis of the process known as carbonation, which is used in the production of carbonated beverages.
In conclusion, when carbon dioxide gas is bubbled through lime water, it initially forms a white precipitate of calcium carbonate in a small amount, turning the lime water milky. With an excess of carbon dioxide, the precipitate dissolves to form a clear solution of calcium bicarbonate.