The Romance of Modern Chemistry

ACIDS AND ALKALIS the so-called “mild” alkalis, carbonate of soda and carbonate of potash. What has been said about an alkali acting as an antidote to an acid will enable the reader to understand that air containing carbon dioxide may be purified by passing over caustic soda. For carbon dioxide is an acid gas, and as such is readily absorbed by an alkali. Hence it is possible to devise an arrangement whereby a person may breathe in a closed space without suffering from accumulated carbon dioxide. It is only necessary that oxygen should be supplied to replace what is absorbed in the lungs, and that the exhaled air should be freed from carbon dioxide by contact with alkali before it is again inhaled. Both these conditions are fulfilled in the so-called oxygen respirating apparatus. This consists of a bag of air carried on the breast and connected by various tubes with (1) the mouth and nostrils, (2) a compartment filled with alkali, and (3) cylinders containing compressed oxygen and carried on the back. Any one provided with a portable apparatus of this description is independent of the surrounding atmos- phere, and may therefore venture into places, entrance into which would ordinarily mean certain death. An equip- ment of this kind was used with success in the rescue work at Courrieres, where, as the reader may remember, a very serious mine disaster occurred not very long ago. But we must return to the question of the well-known alkalis. Solutions of these substances are soapy to the touch, and are extremely useful for cleaning purposes. One thing, however, which should not be cleaned with alkali is the modem aluminium ware used for cooking. Of the few metals which are dissolved by alkalis, aluminium is one. 89