Hold a cold and dry bell-glass over a lighted candle, and watery
vapour will be directly condensed on the cold surface; then close the
mouth of the glass with a card or plate, and turn the mouth uppermost;
remove the card, quickly pour in a little lime-water, a perfectly clear
liquid, and it will instantly become turbid and milky, upon meeting
with the contents of the glass, just as lime-water changes when dropped
into a glass of water.