The Romance of Modern Chemistry

PRODUCTION OF LIGHT AND HEAT lime, the latter is raised to a white heat, and emits a very powerful light. In an electric glow lamp the light proceeds from a carbon filament raised to incandescence, but in this case the source of heat is an electric current, not a flame of burning gas. The electric glow lamp furnishes at the same time an interesting illustration of what has been said about there being two parties to a combustion. The filament in the lamp is made of carbon; there it is, glowing brightly, and yet apparently it suffers no wastage ; it appears to bum, but it is not consumed. Why is this ? Because the other party to a combustion, the oxygen, is absent on this occasion. The lamp has been rendered vacuous during the process of manufacture—that is, the air which it contained was removed—and so no combustion is possible. The tender little filament is protected by its glass cage from the hordes of oxygen molecules that would be only too ready to fall upon it if they had the chance. It must not be supposed that the term combustion is to be applied exclusively to those cases where a carbon- aceous fuel is burned. Many other substances combine readily with the oxygen of the air, and the chemical change involved in this combination produces light and heat Everybody who has seen an underground cavern illumin- ated by the burning of magnesium ribbon knows what an intense light is emitted in this process; and the process is essentially the same as the burning of a piece of char- coal. When charcoal is burned, oxide of carbon (carbon dioxide) is produced; when magnesium is burned, oxide of magnesium (magnesia) is produced. The burning of magnesium illustrates very excellently 114