1308. Lime is the most important of the alkaline earths. The most common form in which it is found is in a state of combination with carbonic acid or fixed air. If a piece of limestone or chalk be thrown into an acid liquid, there will be an effervescence. This is owing to the escape of the carbonic acid gas. The lime becomes dissolved in the liquor. When limestone is strongly heated, the carbonic acid gas is expelled, and then nothing remains but the pure alkaline earth: in this case there is a loss of weight; and, if the fire has been very high, it approaches to one half the weight of the stone; but, in common cases, limestones, if well dried before burning, do not lose much more than 35 to 40 per cent., or from seven to eight parts out of twenty.