Many of the hydro-carbons possess an agreeable odor. Sometimes the woodmen gather the bark and chips of the hickory to smoke hams and shoulders on account of the peculiarly pleasant flavor they impart. In burning, a candle or lamp becomes a gas factory, manufacturing and consuming its own product. The flame consists of three cones. The first, that next to the wick, is composed solely of gas. It is not hot, as can be shown by thrusting the end of a match into it, the match will not ignite. If the match be placed across the flame at the same point it will burn at the edges, but not in the center. A more striking illustration of the fact that the flame is hot only where it comes in contact with the air, can be shown in the following manner: Place on the bottom of an inverted plate some alcohol, in the center set a tiny saucer containing powder; ignite the alcohol, and the powder will remain undisturbed in the center of the surrounding flame until a draft brings the _edge_ of the flame against the powder, when it will at once explode. Look steadily at the flame of an ordinary candle and you can readily discern the three cones; the first is gas, the second gas in rapid combination with the oxygen of the air, the third the products of this combination—watery vapor, carbonic anhydride, and, possibly, some unconsumed carbon. [Illustration: RED FIRE COLORED BY A SALT OF STRONTIUM.[11]] The process that goes on in our stoves is essentially the same. The carbon and hydrogen of the wood or coal unite with the oxygen that passes through the draft. Now note a wonderful provision for our comfort. It has already been remarked that the product of combustion consists of the thing burned, plus oxygen. Suppose, in the case of our fires, this product were a solid, we should then be forced to take out of the stove more material than we put in. The Creator has, however, provided that these resulting materials shall take the form of gas or vapor, so that they can float away. The ashes that remain form but a small part of the whole. The two most common products of combustion are watery vapor and carbonic anhydride. The illumination of our towns and cities has long been accomplished by the use of gas manufactured from coal. Bituminous coal is used for this purpose, and the process consists in heating it to destructive distillation, and afterward condensing and absorbing such portions of the volatilized materials as might clog the gas pipes or interfere with perfect combustion.