PROOFS OF THE PROPERTIES OP LIME.

251

fore proves that carbonate of lime is not dissolved in water butby an excess of carbonic acid.

Experiment IV.

Lime absorbs carbonic acid and water from the atmosphere.

Lime-water remains unchanged in well closed vessels; butwhen exposed to the open air, it becomes covered with a thinpellicle, which, on becoming thicker, breaks and falls to the bot-tom, making room for another new crust, till at last all the limeis separated.

Rationale. ..The cause of the alterations which the lime-water undergoes when exposed to the air, originates from thecarbonic acid of the atmosphere, being powerfully attracted bythe lime dissolved in the water, which thus becomes convertedinto an insoluble carbonate of lime.

The same changes take place with lime itself when in contactwith common air: it first attracts moisture and then carbonicacid; and being thereby gradually slaked, it swells up, splits,falls to pieces, and loses its sharp taste. Its weight is en-creased, and it becomes effervescent. It sensibly returns to-the state of carbonate of lime. The greater the humidity of theair, the speedier these phenomena take place, and are the morestriking. During this gradual slaking, heat is perceptible, bythe absorbed water losing its caloric. It feels therefore warm,and a thermometer immersed in it, rises considerably above thetemperature of the surrounding medium.

Experiment V.

Lime is soluble in water, it tinges blue vegetable colours green.

When more water is added to lime than is necessary toslake it, it becomes at last dissolved. About 300 parts of