Gas Burners Old and New / A historical and descriptive treatise on the progress of invention in gas lighting, embracing an account of the theory of luminous combustion

by Owen Merriman

The thickness of the flame produced by any burner has also an important bearing upon the degree of light afforded; and this property of thickness, again, is dependent upon the width of slit, in the case of batswings (or, in the case of union-jets, upon the size of orifices), and the pressure at which the gas is supplied. The thickness of the flame yielded by any burner will obviously vary inversely with the pressure at which the gas is supplied to it. With a thin flame, all parts of the flame are so completely exposed to the air, that the particles of carbon are no sooner raised to the temperature required to enable them to give out light than they are entirely consumed. With a thicker flame the carbon separated in the midst of the flame exists for a sensibly longer period of time in the white-hot state before it reaches the outside of the flame, and meets with sufficient oxygen for its complete combustion. Thus we find that the best flat-flame burners have comparatively wide orifices; while the pressure at which the gas is delivered from the burner is carefully reduced to the lowest point at which a firm flame is obtained, without smoke. Similarly, in the best Argands the pressure is considerably diminished within the burner, and the gas allowed to issue gently through relatively large holes; while the chimney is carefully adapted to draw upon the surface of the flame just sufficient air to completely consume the quantity of gas which the burner is calculated to deliver.

IMPROVEMENTS IN FLAT-FLAME BURNERS.

Although, there is no doubt, they were made empirically, and in ignorance of the real effects of pressure upon the flame, the first steps towards increasing the efficiency of flat-flame burners were in the right direction of reducing the excessive pressure at which the gas was formerly allowed to burn. They consisted in the adoption of simple arrangements for obstructing the passage of the gas through the burner, and so retarding its flow. The crudeness of the means which were employed is sufficient evidence that the end aimed at was, at best, but dimly discerned. The body of the burner was stuffed with wool, or pieces of wire gauze; which impeded the progress of the gas; reduced the quantity that would otherwise have been consumed; and, consequently, diminished the velocity with which it issued from the burner. Unfortunately, owing to the imperfect methods in use at that day for condensing and purifying the gas, the burners so constructed became choked with the tarry matters held in suspension, and carried forward by the gas; and so, after a comparatively short period of service, were rendered entirely inoperative. But, altogether apart from the inconvenience and loss thus entailed (which, when improved modes of manufacture had removed the cause, ceased to be experienced), the arrangement was ill adapted for the purpose which it was designed to serve. The rough and uneven nature of the material employed to stuff the burner caused the gas to eddy and swirl as it issued into the atmosphere, and prevented it being supplied equally to all parts of the flame. The consequence was that the advantages which ought to have been derived from the diminished pressure were neutralized by the unsteady flow acquired by the stream of gas; and the illuminating power developed by the flame was little improvement upon what could previously be obtained by the manipulation of the tap controlling the supply of gas to the burner. Besides which, from its unevenness, the appearance of the flame was not so satisfactory. It was not until the principles which regulate the production of light from coal gas came to be known and observed in the construction of burners, that a modification of the old idea was arrived at, which enabled the benefits of a reduced pressure to be obtained without any of the attendant evils hitherto experienced.

The first real improvement of the union-jet burner. A modification in the construction of the union-jet which, though slight, was nevertheless a real improvement, appears to have been made at an early period in the history of this burner. Instead of having the top of the burner perfectly flat, it was made slightly concave; more especially at its centre, where the two jets of gas emerge. The effect of this alteration was to enable the stream of gas to spread out better; and thus to cause the flame to become broader at its base. The shape of the flame was thereby improved; and (what is of more consequence) its illuminating power increased, because air was not drawn so readily into the midst of the flame. The value of the arrangement is shown by the fact that it has been retained ever since, and is made use of in the latest and most improved burners of this class.

Prior to 1860, numerous novel contrivances were introduced as "improved" burners; but all were not equally valuable with the simple arrangement just described. The construction of many of them, indeed, betrayed a lamentable ignorance of the first principles of gas combustion. For instance, one is described as "a fishtail with four converging holes; and there is an aperture in the centre of the burner for the admission of atmospheric air into the flame!" Another was a batswing with two or more slits, producing a series of flames amalgamated into one; by which means it was supposed that an improved duty was obtained from the gas—unmindful, or, more probably, in ignorance of the fact that the same quantity of gas, properly consumed through one slit, would yield a better light.

The double-flame burner. A burner which, at different times, and under various names, has been brought repeatedly into notice is the double-flame; consisting of two batswing or union-jet burners set at an angle to each other, so that their flames converge, and merge into one. When two gas flames are made to coalesce in this manner, a greater amount of light is developed than the sum of that yielded by the separate flames; provided that, in the combined flame, the gas is properly consumed, without smoke. The reason for this increase is twofold. First, the increased quantity of gas burnt in one flame enables a higher average temperature to be maintained; and, in addition, a smaller surface of flame is exposed to the cooling action of the atmosphere than when the same quantity of gas is consumed in two flames. Second, the pressure at which the gas burns is diminished, because the initial velocity with which the streams of gas issue from the two burners is expended in impinging against each other, and a thicker flame results; the apparatus being, as far as its effect is concerned, a union-jet burner on a large scale. The increase of light so obtained appears to have been noticed at an early period; as a burner embodying the same principle is described and figured in "Clegg's Treatise," published in 1848. In Clegg's burner the gas issued from two perforated parallel plates inclined to each other; but at a more recent period two fishtail burners were employed, being mounted on separate tubes which branched out to a short distance from each other. Occasionally, for experimental and show purposes, it has been constructed with the two branches hinged together, so as to show the different effects produced when the two burners are used separately and in combination. At the present day it is made, by various makers, as one burner with two nipples, as shown in the annexed illustration; which doubtless is its most perfect form.

Fig. 5.—Duplex Burner.

The advantages of the double flame are not so obvious under the conditions which obtain at the present day as at the period when it was first introduced. The increase of light it affords is most apparent when the gas is being consumed at an excessive pressure. Although, in general, it may be taken that any two flames, when combined, will develop a higher duty, per cubic foot of gas consumed, than separately; yet it would appear that this is not so in every case. When the gas is being consumed at the critical pressure which gives the best results, the flames are so near the smoking point that the slight diminution of pressure experienced when the streams of gas impinge upon each other is sufficient to cause the combined flame to smoke. Moreover, to such a stage of perfection have the ordinary flat-flame burners now been brought, that, for all ordinary consumptions, it may be safely affirmed that equal, if not superior results can be obtained with a single as with a double flame. Where, however, larger quantities of gas are required to be dealt with than can be effectively consumed in a single burner, the principle of combining two or more burners together, so that their flames shall mutually assist each other, may be advantageously employed; as is seen in the combination of flat-flame burners in the large lamps now employed in improved street lighting.