What is milk of sulphur and milk of lime? Why SO2 is difficult to collect over water?

when sublimed sulfur is boiled with lime water ,the lime is removed from the precipitate by washing with dil. HCl ; this is known as milk of sulphur and is used for treatment of various skin orders.
When excess calcium hydroxide is added to limewater, a suspension of calcium hydroxide particles results, giving it a milky aspect, which is commonly known as milk of lime.
It is difficult to collect SO₂over water because it reacts with water.