The Romance of Modern Chemistry

ELEMENTS WITH DOUBLE IDENTITY pierced. In polishing a diamond the only material which is of any use is diamond dust; even emery is too soft to touch it. The phrase “ diamond cut diamond11 has its explanation in what has just been said. Graphite, or black-lead, as it is commonly called, is easily distinguished from the diamond; it is a greyish black substance, crystalline certainly, but soft and soapy to the touch. People gave the name of “ black-lead ” to this form of carbon because they were under the mistaken impiession tliat it contained lead. r11ie power of graphite to give a mark on paper, a property which has found application in the manufacture of pencils, is exhibited also by metallic lead, hence the really erroneous name of “ black-lead.” There are many other ways in which graphite is use- fully applied besides the manufacture of pencils. It is scarcely affected at all by exposure to great heat, and is accordingly made up along with clay into crucibles for use at high temperatures. Then it is used to coat iron- work—grates, for example—in order to protect it from rusting, and at the same time to give it a shiny appear- ance. Another curious use to which graphite is put is the lubricating of machinery working at a high tempera- ture, at which ordinary oil would be unsuitable. Whereas diamond and graphite occur naturally, the various forms of amorphous carbon are generally ob- tained as the products of human operations. Thus wood charcoal is got by the partial combustion of wood, lamp- black is the product of the imperfect combustion of oil, while animal charcoal is obtained by heating bones very strongly. Wood charcoal, lampblack, and animal char- coal or boneblack all consist of amorphous carbon, and are applied in many useful and interesting ways.