The Romance of Modern Chemistry

PRODUCTION OF LIGHT AND HEAT in the process of rusting is not any less than it would be if the oxidation took place rapidly; it is only spread over such a long time that the evolution of heat at any particular moment is not noticeable. Rusting is an example of spontaneous oxidation. It is not necessary to strike a match to start the process ; rust- ing is only too ready, as we often know to our cost, to start on its own account. It is, indeed, essential that carbon dioxide and moisture should be present before rusting can take place, but these substances are both present to some extent in ordinary air, and the only way to keep iron from rusting is either to paint it, or to plate it with some other metal which is less ready to hold traffic with the air. Metals which are commonly used for this purpose are zinc, tin, and nickel. Galvanised iron and tinplate, which are manufactured in such large quantities, are simply iron which has been coated with zinc and tin respectively in order to protect it from corro- sion. Every cyclist knows that so long as the nickel- plating of his handle-bars is intact there is very little tendency to tarnish, but that wherever the protective layer of nickel has been removed rust is not long in putting in an appearance. 117