The Romance of Modern Chemistry

'.""■■'“.■i 1 • 1 SMALL CAUSES; GREAT EFFECTS In the experiments just described the condition of perfect dryness was attained by putting some phosphoric oxide in the tube along with the hydrogen and the oxygen. The oxide in these circumstances acts like so much bird lime, and any water molecules that are flying about are gradually caught. In the absence of water molecules— the mischief-makers, we may term them, or shall we say match-makers ?—the hydrogen and the oxygen are quite callous to each other. So soon, however, as the merest trace of moisture is admitted into the tube, the contents will explode when heated. A few water molecules, in fact, are responsible for all the difference between peace and war, or between the single and wedded states—accord- ing to the way in which the reader prefers to picture the interaction of hydrogen and oxygen. This extraordinary influence of water on chemical change is so remarkable that it is worth while to refer to another interesting experiment that has been made. As the reader is aware, ammonia is a colourless alkaline gas, whereas hydrogen chloride is a colourless acid gas. Like alkalies and acids in general, these two gases interact, forming a salt—ammonium chloride or sal ammoniac—the character- istic and curious feature of the process being the production of this white solid substance from two colourless, invisible gases. It turns out now that this combination between ammonia and hydrogen chloride, which takes place so readily under ordinary circumstances, is not observed when the gases have first been completely freed from all stray water molecules. The ordinary incandescent mantle is an excellent example of the value which may attach to small quantities of foreign material. The mantle consists to the extent of 99 per cent, of thoria, which is the oxide of the metal thorium, 328