The Romance of Modern Chemistry

ACIDS AND ALKALIS thorough is the scrutiny that scarce a single water mole- cule escapes. One property characteristic of acids generally is their power to make carbonates effervesce. Here again domestic resources will be sufficient to supply us with an illustra- tion, for most houses can furnish vinegar and washing-soda. As has been said already, vinegar contains a certain pro- portion of acetic acid, and washing-soda is nothing else than carbonate of soda. When, therefore, we pour a little vinegar on washing-soda we bring together an acid and a carbonate, and the result is the usual one, namely, effervescence due to the liberation of carbon dioxide. This production of gas which occurs when an acid and a carbonate are brought together is applied very ingeni- ously in the chemical fire-engine. The essential parts of this engine are a large closed tank, charged with a solu- tion of bicarbonate of soda, and, inside the tank, a leaden jar containing sulphuric acid. At the proper moment, the acid is tipped into the soda solution, and the carbon dioxide which is generated exerts a pressure sufficient to force water a considerable distance or height. The advan- tage of this fire-engine is obviously that the chemical forces may be brought into play instantaneously ; there is no necessity to wait until the steam is up. The action between an acid and a carbonate may be used in another way in the direct extinction of small fires. It is well known that combustion is not possible in an atmosphere of carbon dioxide, hence if we can surround a piece of burning wood, for example, with such an atmos- phere, we may smother the fire. This is the object of the fire grenades which are to be seen hanging in factories and public buildings. They contain the substances necessary for the production of carbon dioxide, and these