The Romance of Modern Chemistry

ACIDS AND ALKALIS Potash furnishes an interesting illustration of a useful substance coming from unlikely sources, of which two may be mentioned. Wood contains a certain proportion of potash, absorbed from the soil by way of food, and in countries which are well timbered potash is extracted from wood ashes, in which there may be as much as 10 per cent, of the alkali. Its very name is derived from the fact that the wood ashes are dissolved in water and the solution is evaporated down in iron pots. Another and still more strange source from which potash is derived is the fatty matter in the fleece of sheep. This “ suint,” as it is called, contains quite an appreciable amount of the potassium salt of an organic acid, and when this is extracted, evaporated, and strongly heated, potash is left behind. Besides the mild and caustic alkalis which have just been described, there is what is known as the “ volatile alkali ”—ammonia. Although this substance is a gas composed of nitrogen and hydrogen, it is an alkali just as much as caustic potash or washing-soda. It neutralises acids and exerts the same effects as other alkalis on litmus or phenol phthalein. One of the most remarkable properties of ammonia gas is its extreme solubility in water. If a flask quite full of the gas is uncorked with the mouth under water, the latter will rush in and occupy the whole of the flask just as if there had been nothing there at all. Measurements have been made of the solubility, and it has been found that one cubic inch of water will absorb at the ordinary temperature as much as 700 cubic inches of ammonia gas. The solution so obtained may therefore be regarded as a convenient and compact form of ammonia, and it is this which is supplied to us when we ask for ammonia at 90