The Romance of Modern Chemistry

ACIDS AND ALKALIS has united with the quicklime to produce slaked lime: hence its disappearance. The slaking of lime is accompanied by a consider- able increase in bulk, and this fact has been occasion- ally applied in the blasting of coal in fiery mines, where the use of ordinary explosives is dangerous. A so-called “ cartridge ” of quicklime is pressed into a cavity drilled in the coal, and water is then forced in by a pump. The result is that the lime slakes, and the force of the expansion which accompanies the slaking process is such as to plit the surrounding masses of coal—an excellent example this of the chemical energy latent even in the most commonplace materials. We do not usually associate anything very striking with such matter-of-fact substances as lime and water, and yet in their own quiet way they can together do the work for which the aid of a high explosive is generally requisitioned. Lime is very extensively employed in the prepara- tion of building mortar. For this purpose sand and slaked lime are used, and they are made up together with water until the mixture has a pasty consistency. The setting of mortar which occurs a few days after it has been made and applied is simply a process of drying by exposure to the atmosphere. But even after the mortar has set it undergoes a further change—it gradu- ally hardens. This process of hardening is a chemical one, and is due to the slow absorption of carbon dioxide from the atmosphere. It can easily be shown that lime has the power of absorbing carbon dioxide, for if lime water, which is simply a clear solution of slaked lime, is exposed to the air for some time, a white film of chalk collects on 93