234

PROOFS OF THE PROPERTIES OF POTASH.

SECT. II.

EXPERIMENTAL PROOFS

OF

THE PROPERTIES OF POTASH.

Experiment I.

Potash rapidly absorbs water and carbonic acid from, theatmosphere.

If potash be exposed to the air in an open vessel, it soon at-tracts humidity and carbonic acid, augments in weight, becomesliquid, and gradually assumes the state of liquid carbonate ofpotash. To preserve it in a state of purity it must therefore bekept in bottles well stopped and entirely filled with it.

Remark. ..When dry, or fused potash is dissolved in water, itfirst absorbs a certain quantity which it solidifies, caloric is 'evolved, and then the potash dissolves in the excess of W’aterwhich is added. The absorption of water by potash is thereforereally a combination in consequence of the affinity it exercises,and is very different from the simple extension of a salt in a li-quid by solution; this is the reason why sensible caloric is evolv-ed from potash and water, and the rest of the alcalies.

This effect does not take place but when the alcalies are in adry state, or freed from the water of crystallization; for if theyare in a crystallized state when added to the water, cold is pro-duced, because there is no water to be solidified. A solid thenpasses into a st3te of liquidity. This we have considered alreadymore circumstantially under the article Heat.