What reacts with eggshells to give a gas that turns limewater milky?

HCl reacts with eggshells to give a gas that turns limewater milky.
Egg shells contain calcium carbonate in it. When this calcium carbonate is reacted with HCl solution, it releases carbon dioxide gas, turning the lime water milky. Its balanced reaction is given as
                                           $\mathit{CaC}{O}_3 + 2\mathit{HCl }\to \mathit{ CaC}{l}_2 + H_2\mathit{O }+\mathit{ C}{O}_2$