Page:The American Cyclopædia (1879) Volume VII.djvu/262

 254 FLAME the particles of solid carbon. The combustion is completed in the outer cone, d, by the union of carbon and remaining unconsumed gases, with atmospheric oxygen. It is called the mantle, and is much less luminous than the cone last described, the light being principally caused by incandescent gas and vapor. This part of the flame is sometimes confounded with the blue zone at the base, but the mistake can readily be demonstrated by holding a piece of cardboard between the eye and the flame in such a way as to cut off the luminous cone, and thus enable the difference in the character of the light of the two cones in question to be distinguished. The flame of a lamp wick is of course similar to that of a candle ; and a flat flame has the same structure, only the part corresponding to the inner cone is very thin. The blue-colored parts of an ordinary flame are chiefly owing to the combustion of carbonic oxide gas, which may be considered as the transition state of the carbon element during its complete union with atmospheric oxygen and formation of carbonic acid. The upward current of heated gas produced by a flame burning in air, undisturbed by external cur- rents, is quite rapid, as may be observed when smoke is allowed to be carried up with it, and the resistance which it offers to horizontal cur- rents is considerable. The structure and com- position of a candle flame may be demonstrated in several ways. If a fine metallic wire is passed horizontally through the centre, it will soon become incandescent in the luminous cone and mantle on each side of the flame, while that part which is in the dark inner cone will slowly become only slightly red from conduc- tion of heat, or not at all if the wire is very small. If the wire is of steel or iron, after being held for some time in the flame it will be found on examination to have become corroded at those points which were in the mantle and outer part of the luminous cone, in consequence of com- bining with atmospheric oxygen, which it readily does under the influence of incandes- cent heat. That part of the wire which is in the inner cone will not be affected, while that part which is in the inner part of the luminous cone will be covered with lampblack. If a silver or copper wire which has had the sur- face tarnished by oxygen be employed, the tarnish will disappear at those points which are in the inner part of the luminous flame, because the oxygen which had united with the metal is now taken up by the heated free car- bon in the flame. In the outer cone or mantle the coating of oxide will be increased. This furnishes an explanation of the nature of the common or mouth blowpipe flame, which is produced by blowing a fine stream of air through the flame of an oil or alcohol lamp or | a candle, fig. 2. The tip of the blowpipe is usually introduced into the inner cone, and air from the mouth is forced through it, which mingles atmospheric oxygen with the combus- tible gases, and produces complete combustion of all those portions in the line of the jet. The whole flame is directed by the current of the jet, and a current of air surrounding it also passes in the same direction. The whole of the gases of the inner cone are not consumed by the air blown through the pipe (unless it be FIG. 2. too large), but a portion is left to be consumed in the luminous outer hollow cone, c, where it meets with the oxygen of the air. As the oxides of metals are reduced to a metallic state by parting with oxygen to the carbon, the inner flame a is called the reducing flame, and its point 5 is also the hottest point in the whole flame. The outer cone is the oxidizing flame, which varies in quality in different portions, the most effective point for most purposes of oxidation being at the tip, although the flame is used in a variety of ways, depending upon the material under examination and the nature of the substance in which it is held. If a piece of fine wire gauze is held in a horizontal posi- tion and lowered into the flame, the latter will only continue to burn below it, the unconsumed gases passing through, but without sufficient heat to burn. A central dark circle, a section of the inner cone, will then be observed, and also a luminous outer ring, formed of the lumi- nous cone and the mantle. (See fig. 3.) If, while the gauze is held in the flame, a lighted taper be applied to the upper surface, the un- consumed gas will take fire, and the original flame will be nearly restored, the gauze form- ing a horizontal section. If the flame be ex- tinguished by the breath, and while the wick is smoking the gauze be quickly placed a short distance above it, and a lighted taper applied to the upper side, the ascending combustible gases which still issue from the wick and pass through the gauze will take fire, producing a flame above it, which will not extend beneath because the gauze conducts away the heat sufficiently to prevent ignition of the column of gas below. This phenomenon, however, will only last a moment, as the wick soon ceases, in the absence of heat, to furnish com- bustible gases. The experiment can be better made over a jet of common illuminating gas. (See fig. 4.) The flame above the gauze will not be so distinctly divided nor so luminous as in an entire flame, because of the partial mix-