The Romance of Modern Chemistry

HOW FIRE IS MADE while air has access to the vessel, the spirit combines with the oxygen under the influence of the platinum, heat is produced, the platinum glows, and finally the spirit bursts into flame. Reference has just been made to the very high cata- lytic power of platinum when it is in a finely-divided condition. Generally speaking, it may be said that finely-divided matter behaves differently in many respects from compact matter of the same kind. It is, for example, a consequence of the law of gravitation that solid particles in the air soon fall to the ground, but if they are infinitesimally small they may travel quite a long distance without coining to earth. Thus the beautiful sunsets seen in England in 1883 were attri- buted to the presence of very fine dust in the atmos- phere, carried all the way from a volcanic eruption on the other side of the globe. In regard also to combustion finely-divided substances have somewhat peculiar manners. Everybody would regard iron and lead as elements of the most staid and sober temperament; and yet it is possible to obtain these metals in a state of such fine division, that when they are thrown out of any vessel into the air, they take fire of their own accord. The finely-divided sub- stance has relatively a much greater surface than the compact substance, and the rate of rusting or oxida- tion is thereby so much increased that incandescence is observed ; the process of combustion, which is slow under ordinary conditions, becomes very rapid. The pheno- menon might be described as “ spontaneous combustion,” but the reader should clearly understand that the chemi- cal change which takes place when finely divided iron or lead take fire in air is exactly the same as when 127