The Romance of Modern Chemistry

MORE ABOUT FUEL bowl of a clay pipe with little bits of coal, blocking up the mouth of the bowl with clay, and then heating it in a fire. When this is done, a gas will be found issuing from the end of the pipe stem, which will bum with a luminous flame. This gas is essentially the same as coal gas, and the method by which it has been obtained is destructive distillation—the process by which also char- coal, coke, and coal gas are obtained from the natural fuels. It is, of course, necessary that the natural fuels which are undergoing destructive distillation should be excluded from contact with air during the process—other- wise combustion would take place. What occurs then is that the carbon compounds in the natural fuel are chemically decomposed by the action of heat; the atoms of carbon, hydrogen, and oxygen are re-arranged, and new products are formed which did not exist as such in the original fuel. The chemical decomposition which takes place in the dry distillation of wood or coal is exceedingly complex, and the number of products that can ultimately be obtained is very large indeed. But although this is so, the first crude products are only four in number, namely, gas, watciy liquid, tar, and residue, these differing in character according as wood or coal is being subjected to distillation. In the case of wood the process is sometimes carried out by stacking the wood, burning part of it, and using the heat so obtained to decompose the rest. This is a wasteful method, so far as most of the products are con- cerned, for no provision is made to catch those which are volatile. The residue is known as wood charcoal, and consists very largely of carbon, with small quantities of hydrogen, oxygen, and nitrogen, and a little ash or 143