COMBUSTION OF ACETYLENE IN LUMINOUS BURNERS—THEIR DISPOSITION
NATURE OF LUMINOUS FLAMES.—When referring to methods of obtaining artificial light by means of processes involving combustion or oxidation, the term "incandescence" is usually limited to those forms of burner in which some extraneous substance, such as a "mantle," is raised to a brilliant white heat. Though convenient, the phrase is a mere convention, for all artificial illuminants, even including the electric light, which exhibit a useful degree of intensity depend on the same principle of incandescence. Adopting the convention, however, an incandescent burner is one in which the fuel burns with a non-luminous or atmospheric flame, the light being produced by causing that flame to play upon some extraneous refractory body having the property of emitting much light when it is raised to a sufficiently high temperature; while a luminous burner is one in which the fuel is allowed to combine with atmospheric oxygen in such a way that one or more of the constituents in the gas evolves light as it suffers combustion. From the strictly chemical point of view the light-giving substance in the incandescent flame lasts indefinitely, for it experiences no change except in temperature; whereas the light-giving substance in a luminous flame lasts but for an instant, for it only evolves light during the act of its combination with the oxygen of the atmosphere. Any fluid combustible which burns with a flame can be made to give light on the incandescent system, for all such materials either burn naturally, or can be made to burn with a non- luminous flame, which can be employed to raise the temperature of some mantle; but only those fuels can be burnt on the self-luminous system which contain some ingredient that is liberated in the elemental state in the flame, the said ingredient being one which combines energetically with oxygen so as to liberate much local heat. In practice, just as there are only two or three substances which are suitable for the construction of an incandescent mantle, so there is only one which renders a flame usefully self-luminous, viz., carbon; and therefore only such fuels as contain carbon among their constituents can be burnt so as to produce light without the assistance of the mantle. But inasmuch as it is necessary for the evolution of light by the combustion of carbon that that carbon shall be in the free state, only those carbonaceous fuels yield light without the mantle in which the carbonaceous ingredient is dissociated into its elements before it is consumed. For instance, alcohol and carbon monoxide are both combustible, and both contain carbon; but they yield non-luminous flames, for the carbon burns to carbon dioxide in ordinary conditions without assuming the solid form; ether, petroleum, acetylene, and some of the hydrocarbons of coal-gas do emit light on combustion, for part of their carbon is so liberated. The quantity of light emitted by the glowing substance increases as the temperature of that substance rises: the gain in light being equal to the fifth or higher power of the gain in heat; [Footnote: Calculated from absolute zero.] therefore unnecessary dissipation of heat from a flame is one of the most important matters to be guarded against if that flame is to be an economical illuminant. But the amount of heat liberated when a certain weight (or volume) of a particular fuel combines with a sufficient quantity of oxygen to oxidise it wholly is absolutely fixed, and is exactly the same whether that fuel is made to give a luminous or a non-luminous flame. Nevertheless the atmospheric flame given by a certain fuel may be appreciably hotter than its luminous flame, because the former is usually smaller than the latter. Unless the luminous flame of a rich fuel is made to expose a wide surface to the air, part of its carbon may escape ultimate combustion; soot or smoke may be produced, and some of the most valuable heat-giving substance will be wasted. But if the flame is made to expose a large surface to the air, it becomes flat or hollow in shape instead of being cylindrical and solid, and therefore in proportion to its cubical capacity it presents to the cold air a larger superficies, from which loss of heat by radiation, &c., occurs. Being larger, too, the heat produced is less concentrated.
It does not fall within the province of the present book to discuss the relative merits of luminous and incandescent lighting; but it may be remarked that acetylene ranks with petroleum against coal-gas, carburetted or non-carburetted water-gas, and semi-water-gas, in showing a comparatively small degree of increased efficiency when burnt under the mantle. Any gas which is essentially composed of carbon monoxide or hydrogen alone (or both together) burns with a non-luminous flame, and can therefore only be used for illuminating purposes on the incandescent system; but, broadly speaking, the higher is the latent illuminating power of the gas itself when burnt in a non-atmospheric burner, the less marked is the superiority, both from the economical and the hygienic aspect, of its incandescent flame. It must be remembered also that only a gas yields a flame when it is burnt; the flame of a paraffin lamp and of a candle is due to the combustion of the vaporised fuel. Methods of burning acetylene under the mantle are discussed in Chapter IX.; here only self-luminous flames are being considered, but the theoretical question of heat economy applies to both processes.
Heat may be lost from a flame in three several ways: by direct radiation and conduction into the surrounding air, among the products of combustion, and by conduction into the body of the burner. Loss of heat by radiation and conduction to the air will be the greater as the flame exposes a larger surface, and as a more rapid current of cold air is brought into proximity with the flame. Loss of heat by conduction, into the burner will be the greater as the material of which the burner is constructed is a better conductor of heat, and as the mass of material in that burner is larger. Loss of heat by passage into the combustion products will also be greater as these products are more voluminous; but the volume of true combustion products from any particular gas is a fixed quantity, and since these products must leave the flame at the temperature of that flame—where the highest temperature possible is requisite—it would seem that no control can be had over the quantity of heat so lost. However, although it is not possible in practice to supply a flame with too little air, lest some of its carbon should escape consumption and prove a nuisance, it is very easy without conspicuous inconvenience to supply it with too much; and if the flame is supplied with too much, there is an unnecessary volume of air passing through it to dilute the true combustion products, which air absorbs its own proper proportion of heat. It is only the oxygen of the air which a flame needs, and this oxygen is mixed with approximately four times its volume of nitrogen; if, then, only a small excess of oxygen (too little to be noticeable of itself) is admitted to a flame, it is yet harmful, because it brings with it four times its volume of nitrogen, which has to be raised to the same temperature as the oxygen. Moreover, the nitrogen and the excess of oxygen occupy much space in the flame, making it larger, and distributing that fixed quantity of heat which it is capable of generating over an unnecessarily large area. It is for this reason that any gas gives so much brighter a light when burnt in pure oxygen than in air, (1) because the flame is smaller and its heat more concentrated, and (2) because part of its heat is not being wasted in raising the temperature of a large mass of inert nitrogen. Thus, if the flame of a gas which naturally gives a luminous flame is supplied with an excess of air, its illuminating value diminishes; and this is true whether that excess is introduced at the base of the actual flame, or is added to the gas prior to ignition. In fact the method of adding some air to a naturally luminous gas before it arrives at its place of combustion is the principle of the Bunsen burner, used for incandescent lighting and for most forms of warming and cooking stoves. A well-made modern atmospheric burner, however, does not add an excess of air to the flame, as might appear from what has been said; such a burner only adds part of the air before and the remainder of the necessary quantity after the point of first ignition—the function of the primary supply being merely to insure thorough admixture and to avoid the production of elemental carbon within the flame.
ILLUMINATING POWER.—It is very necessary to observe that, as the combined losses of heat from a flame must be smaller in proportion to the total heat produced by the flame as the flame itself becomes larger, the more powerful and intense any single unit of artificial light is, the more economical does it become, because economy of heat spells economy of light. Conversely, the more powerful and intense any single unit of light is, the more is it liable to injure the eyesight, the deeper and, by contrast, the more impenetrable are the shadows it yields, and the less pleasant and artistic is its effect in an occupied room. For economical reasons, therefore, one large central source of light is best in an apartment, but for physiological and æsthetic reasons a considerable number of correspondingly smaller units are preferable. Even in the street the economical advantage of the single unit is outweighed by the inconvenience of its shadows, and by the superiority of a number of evenly distributed small sources to one central large source of light whenever the natural transmission of light rays through the atmosphere is interfered with by mist or fog. The illuminating power of acetylene is commonly stated to be "240 candles" (though on the same basis Wolff has found it to be about 280 candles). This statement means that when acetylene is consumed in the most advantageous self-luminous burner at the most advantageous rate, that rate (expressed in cubic feet per hour) is to 5 in the same ratio as the intensity of the light evolved (expressed in standard candles) is to the said "illuminating power." Thus, Wolff found that when acetylene was burnt in the "0000 Bray" fish- tail burner at the rate of 1.377 cubic feet per hour, a light of 77 candle-power was obtained. Hence, putting x to represent the illuminating power of the acetylene in standard candles, we have:
1.377 / 5 = 77 / x hence x = 280.
Therefore acetylene is said to have, according to Wolff, an illuminating power of about 280 candles, or according to other observers, whose results have been commonly quoted, of 240 candles. The same method of calculating the nominal illuminating power of a gas is applied within the United Kingdom in the case of all gases which cannot be advantageously burnt at the rate of 5 cubic feet per hour in the standard burner (usually an Argand). The rate of 5 cubic feet per hour is specified in most Acts of Parliament relating to gas-supply as that at which coal-gas is to be burnt in testings of its illuminating power; and the illuminating power of the gas is defined as the intensity, expressed in standard candles, of the light afforded when the gas is burnt at that rate. In order to make the values found for the light evolved at more advantageous rates of consumption by other descriptions of gas—such as oil-gas or acetylene—comparable with the "illuminating power" of coal- gas as defined above, the values found are corrected in the ratio of the actual rate of consumption to 5 cubic feet per hour.
In this way the illuminating power of 240 candles has been commonly assigned to acetylene, though it would be clearer to those unfamiliar with the definition of illuminating power in the Acts of Parliament which regulate the testing of coal-gas, if the same fact were conveyed by stating that acetylene affords a maximum illuminating power of 48 candles (i.e., 240 / 5) per cubic foot. Actually, by misunderstanding of the accepted though arbitrary nomenclature of gas photometry, it has not infrequently been assorted or implied that a cubic foot of acetylene yields a light of 240 candle-power instead of 48 candle-power. It should, moreover, be remembered that the ideal illuminating power of a gas is the highest realisable in any Argand or flat-flame burner, while the said burner may not be a practicable one for general use in house lighting. Thus, the burners recommended for general use in lighting by acetylene do not develop a light of 48 candles per cubic foot of gas consumed, but considerably less, as will appear from the data given later in this chapter.
It has been stated that in order to avoid loss of heat from a flame through the burner, that burner should present only a small mass of material (i.e., be as light in weight as possible), and should be constructed of a bad heat-conductor. But if a small mass of a material very deficient in heat-conducting properties comes in contact with a flame, its temperature rises seriously and may approach that of the base of the flame itself. In the case of coal-gas this phenomenon is not objectionable, is even advantageous, and it explains why a burner made of steatite, which conducts heat badly, in always more economical (of heat and therefore of light) than an iron one. In the case of acetylene the same rule should, and undoubtedly does, apply also; but it is complicated, and its effect sometimes neutralised, by a peculiarity of the gas itself. It has been shown in Chapters II. and VI. that acetylene polymerises under the influence of heat, being converted into other bodies of lower illuminating power, together with some elemental carbon. If, now, acetylene is fed into a burner which, being composed of some material like steatite possessed of low heat-conducting and radiating powers, is very hot, and if the burner comprises a tube of sensible length, the gas that actually arrives at the orifice may no longer be pure acetylene, but acetylene diluted with inferior illuminating agents, and accompanied by a certain proportion of carbon. Neglecting the effect of this carbon, which will be considered in the following paragraph, it is manifest that the acetylene issuing from a hot burner—assuming its temperature to exceed the minimum capable of determining polymerisation— may emit less light per unit of volume than the acetylene escaping from a cold burner. Proof of this statement is to be found in some experiments described by Bullier, who observed that when a small "Manchester" or fish-tail burner was allowed to become naturally hot, the quantity of gas needed to give the light of one candle (uncorrected) was 1.32 litres, but when the burner was kept cool by providing it with a jacket in which water was constantly circulating, only 1.13 litres of acetylene were necessary to obtain the same illuminating value, this being an economy of 16 per cent.
EARLY BURNERS.—One of the chief difficulties encountered in the early days of the acetylene industry was the design of a satisfactory burner which should possess a life of reasonable length. The first burners tried were ordinary oil-gas jets, which resemble the fish-tails used with coal- gas, but made smaller in every part to allow for the higher illuminating power of the oil-gas or acetylene per unit of volume. Although the flames they gave were very brilliant, and indeed have never been surpassed, the light quickly fell off in intensity owing to the distortion of their orifices caused by the deposition of solid matter at the edges. Various explanations have been offered to account for the precipitation of solid matter at the jets. If the acetylene passes directly to the burner from a generator having carbide in excess without being washed or filtered in any way, the gas may carry with it particles of lime dust, which will collect in the pipes mainly at the points where they are constricted; and as the pipes will be of comparatively large bore until the actual burner is readied, it will be chiefly at the orifices where the deposition occurs. This cause, though trivial, is often overlooked. It will be obviated whenever the plant is intelligently designed. As the phosphoric anhydride, or pentoxide, which is produced when a gas containing phosphorus burns, is a solid body, it may be deposited at the burner jets. This cause may be removed, or at least minimised, by proper purification of the acetylene, which means the removal of phosphorus compounds. Should the gas contain hydrogen silicide siliciuretted hydrogen), solid silica will be produced similarly, and will play its part in causing obstruction. According to Lewes the main factor in the blocking of the burners is the presence of liquid polymerised products in the acetylene, benzene in particular; for he considers that these bodies will be absorbed by the porous steatite, and will be decomposed under the influence of heat in that substance, saturating the steatite with carbon which, by a "catalytic" action presumably, assists in the deposition of further quantities of carbon in the burner tube until distortion of the flame results. Some action of this character possibly occurs; but were it the sole cause of blockage, the trouble would disappear entirely if the gas were washed with some suitable heavy oil before entering the burners, or if the latter were constructed of a non-porous material. It is certainly true that the purer is the acetylene burnt, both as regards freedom from phosphorus and absence of products of polymerisation, the longer do the burners last; and it has been claimed that a burner constructed at its jets of some non-porous substance, e.g., "ruby," does not choke as quickly as do steatite ones. Nevertheless, stoppages at the burners cannot be wholly avoided by these refinements. Gaud has shown that when pure acetylene is burnt at the normal rate in 1-foot Bray jets, growths of carbon soon appear, but do not obstruct the orifices during 100 hours' use; if, however, the gas-supply is checked till the flame becomes thick, the growths appear more quickly, and become obstructive after some 60 hours' burning. On the assumption that acetylene begins to polymerise at a temperature of 100° C., Gaud calculates that polymerisation cannot cause blocking of the burners unless the speed of the passing gas is so far reduced that the burner is only delivering one- sixth of its proper volume. But during 1902 Javal demonstrated that on heating in a gas-flame one arm of a twin, non-injector burner which had been and still was behaving quite satisfactorily with highly purified acetylene, growths were formed at the jet of that arm almost instantaneously. There is thus little doubt that the principal cause of this phenomenon is the partial dissociation of the acetylene (i.e., decomposition into its elements) as it passes through the burner itself; and the extent of such dissociation will depend, not at all upon the purity of the gas, but upon the temperature of the burner, upon the readiness with which the heat of the burner is communicated to the gas, and upon the speed at which the acetylene travels through the burner.
Some experiments reported by R. Granjon and P. Mauricheau-Beaupré in 1906 indicate, however, that phosphine in the gas is the primary cause of the growths upon non-injector burners. According to these investigators the combustion of the phosphine causes a deposit at the burner orifices of phosphoric acid, which is raised by the flame to a temperature higher than that of the burner. This hot deposit then decomposes some acetylene, and the carbon deposited therefrom is rendered incombustible by the phosphoric acid which continues to be produced from the combustion of the phosphine in the gas. The incombustible deposit of carbon and phosphoric acid thus produced ultimately chokes the burner.
It will appear in Chapter XI. that some of the first endeavours to avoid burner troubles were based on the dilution of the acetylene with carbon dioxide or air before the gas reached the place of combustion; while the subsequent paragraphs will show that the same result is arrived at more satisfactorily by diluting the acetylene with air during its actual passage through the burner. It seems highly probable that the beneficial effect of the earliest methods was due simply or primarily to the dilution, the molecules of the acetylene being partially protected from the heat of the burner by the molecules of a gas which was not injured by the high temperature, and which attracted to itself part of the heat that would otherwise have been communicated to the hydrocarbon. The modern injector burner exhibits the same phenomenon of dilution, and is to the same extent efficacious in preventing polymerisation; but inasmuch as it permits a larger proportion of air to be introduced, and as the addition is made roughly half-way along the burner passage, the cold air is more effectual in keeping the former part of the tip cool, and in jacketing the acetylene during its travel through the latter part, the bore of which is larger than it otherwise would be.
INJECTOR AND TWIN-FLAME BURNERS.—In practice it is neither possible to cool an acetylene burner systematically, nor is it desirable to construct it of such a large mass of some good heat conductor that its temperature always remains below the dissociation point of the gas. The earliest direct attempts to keep the burner cool were directed to an avoidance of contact between the flame of the burning acetylene and the body of the jet, this being effected by causing the current of acetylene to inject a small proportion of air through lateral apertures in the burner below the point of ignition. Such air naturally carries along with it some of the heat which, in spite of all precautions, still reaches the burner; but it also apparently forms a temporary annular jacket round the stream of gas, preventing it from catching fire until it has arrived at an appreciable distance from the jet. Other attempts were made by placing two non- injector jets in such mutual positions that the two streams of gas met at an angle, there to spread fan-fashion into a flat flame. This is really nothing but the old fish-tail coal-gas burner—which yields its flat flame by identical impingement of two gas streams—modified in detail so that the bulk of the flame should be at a considerable distance from the burner instead of resting directly upon it. In the fish-tail the two orifices are bored in the one piece of steatite, and virtually join at their external ends; in the acetylene burner, two separate pieces of steatite, three-quarters of an inch or more apart, carried by completely separate supports, are each drilled with one hole, and the flame stands vertically midway between them. The two streams of gas are in one vertical plane, to which the vertical plane of the flame is at right angles. Neither of these devices singly gave a solution of the difficulty; but by combining the two—the injector and the twin-flame principle—the modern flat-flame acetylene burner has been evolved, and is now met with in two slightly different forms known as the Billwiller and the Naphey respectively. The latter apparently ought to be called the Dolan.
[Illustration: FIG. 8.—TYPICAL ACETYLENE BURNERS.]
The essential feature of the Naphey burner is the tip, which is shown in longitudinal section at A in Fig. 8. It consists of a mushroom headed cylinder of steatite, drilled centrally with a gas passage, which at its point is of a diameter suited to pass half the quantity of acetylene that the entire burner is intended to consume. The cap is provided with four radial air passages, only two of which are represented in the drawing; these unite in the centre of the head, where they enter into the longitudinal channel, virtually a continuation of the gas-way, leading to the point of combustion by a tube wide enough to pass the introduced air as well as the gas. Being under some pressure, the acetylene issuing from the jet at the end of the cylindrical portion of the tip injects air through the four air passages, and the mixture is finally burnt at the top orifice. As pointed out in Chapter VII., the injector jet is so small in diameter that even if the service-pipes leading to the tip contain an explosive mixture of acetylene and air, the explosion produced locally if a light is applied to the burner cannot pass backwards through that jet, and all danger is obviated. One tip only of this description evidently produces a long, jet-like flame, or a "rat-tail," in which the latent illuminating power of the acetylene is not developed economically. In practice, therefore, two of these tips are employed in unison, one of the commonest methods of holding them being shown at B. From each tip issues a stream of acetylene mixed with air, and to some extent also surrounded by a jacket of air; and at a certain point, which forms the apex of an isosceles right-angled triangle having its other angles at the orifices of the tips, the gas streams impinge, yielding a flat flame, at right- angles, as mentioned before, to the plane of the triangle. If the two tips are three-quarters of an inch apart, and if the angle of impingement is exactly 90°, the distance of each tip from the base of the flame proper will be a trifle over half an inch; and although each stream of gas does take fire and burn somewhat before meeting its neighbour, comparatively little heat is generated near the body of the steatite. Nevertheless, sufficient heat is occasionally communicated to the metal stems of these burners to cause warping, followed by a want of alignment in the gas streams, and this produces distortion of the flame, and possibly smoking. Three methods of overcoming this defect have been used: in one the arms are constructed entirely of steatite, in another they are made of such soft metal as easily to be bent back again into position with the fingers or pliers, in the third each arm is in two portions, screwing the one into the other. The second type is represented by the original Phôs burner, in which the curved arms of B are replaced by a pair of straight divergent arms of thin, soft tubing, joined to a pair of convergent wider tubes carrying the two tips. The third type is met with in the Drake burner, where the divergent arms are wide and have an internal thread into which screws an external thread cut upon lateral prolongations of the convergent tubes. Thus both the Phôs and the Drake burner exhibit a pair of exposed elbows between the gas inlet and the two tips; and these elbows are utilised to carry a screwed wire fastened to an external milled head by means of which any deposit of carbon in the burner tubes can be pushed out. The present pattern of the Phôs burner is shown in Fig. 9, in which A is the burner tip, B the wire or needle, and C the milled head by which the wire is screwed in and out of the burner tube.
[Illustration: FIG. 9.—IMPROVED PHÔS BURNER.]
[Illustration: FIG. 10.—"WONDER" SINGLE AND TWO-FLAME BURNERS.]
[Illustration: FIG. 11.—"SUPREMA" NO. 266651, TWO-FLAME BURNER.]
[Illustration: FIG. 12.—BRAY'S MODIFIED NAPHEY INJECTOR BURNER TIP.]
[Illustration: FIG. 13.—BRAY'S "ELTA" BURNER.]
[Illustration: FIG. 14.—BRAY'S "LUTA" BURNER.]
[Illustration: FIG. 15.—BRAY'S "SANSAIR" BURNER.]
[Illustration: FIG. 16.—ADJUSTABLE "KONA" BURNER.]
In the original Billwiller burner, the injector gas orifice was brought centrally under a somewhat larger hole drilled in a separate sheet of platinum, the metal being so carried as to permit entry of air. In order to avoid the expense of the platinum, the same principle was afterwards used in the design of an all-steatite head, which is represented at D in Fig. 8. The two holes there visible are the orifices for the emission of the mixture of acetylene with indrawn air, the proper acetylene jets lying concentrically below these in the thicker portions of the heads. These two types of burner have been modified in a large number of ways, some of which are shown at C, E, and F; the air entering through saw- cuts, lateral holes, or an annular channel. Burners resembling F in outward form are made with a pair of injector jets and corresponding air orifices on each head, so as to produce a pair of names lying in the same plane, "end-on" to one another, and projecting at either side considerably beyond the body of the burner; these have the advantage of yielding no shadow directly underneath. A burner of this pattern, viz., the "Wonder," which is sold in this country by Hannam's, Ltd., is shown in Fig. 10, alongside the single-flame "Wonder" burner, which is largely used, especially in the United States. Another two-flame burner, made of steatite, by J. von Schwarz of Nuremberg, and sold by L. Wiener of London, is shown in Fig. 11. Burners of the Argand type have also been manufactured, but have been unsuccessful. There are, of course, endless modifications of flat-flame burners to be found on the markets, but only a few need be described. A device, which should prove useful where it may be convenient to be able to turn one or more burners up or down from the same common distant spot, has been patented by Forbes. It consists of the usual twin-injector burner fitted with a small central pinhole jet; and inside the casing is a receptacle containing a little mercury, the level of which is moved by the gas pressure by an adaptation of the displacement principle. When the main is carrying full pressure, both of the jets proper are alight, and the burner behaves normally, but if the pressure is reduced to a certain point, the movement of the mercury seals the tubes leading to the main jets, and opens that of the pilot flame, which alone remains alight till the pressure is increased again. Bray has patented a modification of the Naphey injector tip, which is shown in Fig. 12. It will be observed that the four air inlets are at right-angles to the gas-way; but the essential feature of the device is the conical orifice. By this arrangement it is claimed that firing back never occurs, and that the burner can be turned down and left to give a small flame for considerable periods of time without fear of the apertures becoming choked or distorted. As a rule burners of the ordinary type do not well bear being turned down; they should either be run at full power or extinguished completely. The "Elta" burner, made by Geo. Bray and Co., Ltd., which is shown in Fig. 13, is an injector or atmospheric burner which may be turned low without any deposition of carbon occurring on the tips. A burner of simple construction but which cannot be turned low is the "Luta," made by the same firm and shown in Fig. 14. Of the non- atmospheric type the "Sansair," also made by Geo. Bray and Co., Ltd., is extensively used. It is shown in Fig. 15. In order to avoid the warping, through the heat of the flame, of the arms of burners which sometimes occurs when they are made of metal, a number of burners are now made with the arms wholly of steatite. One of the best-known of these, of the injector type, is the "Kona," made by Falk, Stadelmann and Co., of London. It is shown in Fig. 16, fitted with a screw device for adjusting the flow of gas, so that when this adjuster has been set to give a flame of the proper size, no further adjustment by means of the gas-tap is necessary. This saves the trouble of manipulating the tap after the gas is lighted. The same adjusting device may also be had fitted to the Phôs burner (Fig. 9) or to the "Orka" burner (Fig. 17), which is a steatite- tip injector burner with metal arms made by Falk, Stadelmann and Co., Ltd. A burner with steatite arms, made by J. von Schwarz of Nuremberg, and sold in this country by L. Wiener of London, is shown in Fig. 18.
[Illustration: FIG. 17.—"ORKA" BURNER.]
[Illustration: FIG. 18.—"SUPREMA" NO. 216469 BURNER.]
ILLUMINATING DUTY.—The illuminating value of ordinary self-luminous acetylene burners in different sizes has been examined by various photometrists. For burners of the Naphey type Lewes gives the following table:
___________________________________________________________ | | | | | | | | | Gas | | Candles | | Burner. | Pressure, | Consumed, | Light in | per | | | Inches | Cubic Feet | Candles. | Cubic Foot. | | | | per Hour. | | | |_________|___________|____________|__________|_____________| | | | | | | | No. 6 | 2.0 | 0.155 | 0.794 | 5.3 | | " 8 | 2.0 | 0.27 | 3.2 | 11.6 | | " 15 | 2.0 | 0.40 | 8.0 | 20.0 | | " 25 | 2.0 | 0.65 | 17.0 | 26.6 | | " 30 | 2.0 | 0.70 | 23.0 | 32.85 | | " 42 | 2.0 | 1.00 | 34.0 | 34.0 | |_________|___________|____________|__________|_____________|
From burners of the Billwiller type Lewes obtained in 1899 the values:
___________________________________________________________ | | | | | | | | | Gas | | Candles | | Burner. | Pressure, | Consumed, | Light in | per | | | Inches | Cubic Feet | Candles. | Cubic Foot. | | | | per Hour. | | | |_________|___________|____________|__________|_____________| | | | | | | | No. 1 | 2.0 | 0.5 | 7.0 | 11.0 | | " 2 | 2.0 | 0.75 | 21.0 | 32.0 | | " 3 | 2.0 | 0.75 | 28.0 | 37.3 | | " 4 | 3.0 | 1.2 | 48.0 | 40.0 | | " 5 | 3.5 | 2.0 | 76.0 | 38.0 | |_________|___________|____________|__________|_____________|
Neuberg gives these figures for different burners (1900) as supplied by
Pintsch:
Pintsch:
______________________________________________________________________ | | | | | | | | Gas | | Candles | |"w | Burner. | Pressure, | Consumed, | Light in | per | | | Inches | Cubic Feet | Candles. | Cubic Foot. | | | | per Hour. | | | |____________________|___________|____________|__________|_____________| | | | | | | | No. 0, slit burner | 3.9 | 1.59 | 59.2 | 37.3 | | " 00000 fishtail | 1.6 | 0.81 | 31.2 | 38.5 | | Twin burner No. 1 | 3.2 | 0.32 | 13.1 | 40.8 | | " " " 2 | 3.2 | 0.53 | 21.9 | 41.3 | | " " " 3 | 3.2 | 0.74 | 31.0 | 41.9 | | " " " 4 | 3.2 | 0.95 | 39.8 | 41.9 | |____________________|___________|____________|__________|_____________|
The actual candle-power developed by each burner was not quoted by Neuberg, and has accordingly been calculated from his efficiency values. It is noteworthy, and in opposition to what has been found by other investigators as well as to strict theory, that Neuberg represents the efficiencies to be almost identical in all sizes of the same description of burner, irrespective of the rate at which it consumes gas.
Writing in 1902, Capelle gave for Stadelmann's twin injector burners the following figures; but as he examined each burner at several different pressures, the values recorded in the second, third, and fourth columns are maxima, showing the highest candle-power which could be procured from each burner when the pressure was adjusted so as to cause consumption to proceed at the most economical rate. The efficiency values in the fifth column, however, are the mean values calculated so as to include all the data referring to each burner. Capelle's results have been reproduced from the original on the basis that 1 bougie décimale equals 0.98 standard English candle, which is the value he himself ascribes to it (1 bougie décimale equals 1.02 candles is the value now accepted).
_____________________________________________________________________ | | | | | | | Nominal | Best | Actual Consumption | Maximum | Average | | Consumption,| Pressure| at Stated Pressure. | Light in | Candles per| | Litres. | Inches. | Cubic Feet per Hour.| Candles. | Cubic Foot.| |_____________|_________|_____________________|__________|____________| | | | | | | | 10 | 3.5 | 0.40 | 8.4 | 21.1 | | 15 | 2.8 | 0.46 | 16.6 | 33.3 | | 20 | 3.9 | 0.64 | 25.1 | 40.0 | | 25 | 3.5 | 0.84 | 37.8 | 46.1 | | 30 | 3.5 | 0.97 | 48.2 | 49.4 | |_____________|_________|_____________________|__________|____________|
Some testings of various self-luminous burners of which the results were reported by R. Granjon in 1907, gave the following results for the duty of each burner, when the pressure was regulated for each burner to that which afforded the maximum illuminating duty. The duty in the original paper is given in litres per Carcel-hour. The candle has been taken as equal to 0.102 Carcel for the conversion to candles per cubic foot.
___________________________________________________________________ | | | | | | | Nominal | Best | Duty. Candles | | Burner. | Consumption.| Pressure. | per cubic foot. | |_______________________|_____________|__________ |_________________| | | | | | | | Litres. | Inches. | | | Twin . . . . | 10 | 2.76 | 21.2 | | " . . . . | 20 | 2.76 | 23.5 | | " . . . . | 25 | 3.94 | 30.2 | | " . . . . | 30 | 3.94-4.33 | 44.8 | | ", (pair of flames) | 35 | 3.55-3.94 | 45.6 | | Bray's "Manchester" | 6 | 1.97 | 18.8 | | " | 20 | 1.97 | 35.6 | | " | 40 | 2.36 | 42.1 | | Rat-tail . . . | 5 | 5.5 | 21.9 | | " . . . | 8 | 4.73 | 25.0 | | Slit or batswing . | 30 | 1.97-2.36 | 37.0 | |_______________________|_____________|___________|_________________|
Granjon has concluded from his investigations that the Manchester or fish-tail burners are economical when they consume 0.7 cubic foot per hour and when the pressure is between 2 and 2.4 inches. When these burners are used at the pressure most suitable for twin burners their consumption is about one-third greater than that of the latter per candle-hour. The 25 to 35 litres-per-hour twin burners should be used at a pressure higher by about 1 inch than the 10 to 20 litres-per-hour twin burners.
At the present time, when the average burner has a smaller hourly consumption than 1 foot per hour, it is customary in Germany to quote the mean illuminating value of acetylene in self-luminous burners as being 1 Hefner unit per 0.70 litre, which, taking
1 Hefner unit = 0.913 English candle
1 English candle = 1.095 Hefner units,
works out to an efficiency of 37 candles per foot in burners probably consuming between 0.5 and 0.7 foot per hour.
Even when allowance is made for the difficulties in determining illuminating power, especially when different photometers, different standards of light, and different observers are concerned, it will be seen that these results are too irregular to be altogether trustworthy, and that much more work must be done on this subject before the economy of the acetylene flame can be appraised with exactitude. However, as certain fixed data are necessary, the authors have studied those and other determinations, rejecting some extreme figures, and averaging the remainder; whence it appears that on an average twin-injector burners of different sizes should yield light somewhat as follows:
_______________________________________________________ | | | | | Size of Burner in | Candle-power | Candles | | Cubic Feet per Hour. | Developed. | per Cubic Foot. | |______________________|______________|_________________| | | | | | 0.5 | 18.0 | 35.9 | | 0.7 | 27.0 | 38.5 | | 1.0 | 45.6 | 45.6 | |______________________|______________|_________________|
In the tabular statement in Chapter I. the 0.7-foot burner was taken as the standard, because, considering all things, it seems the best, to adopt for domestic purposes. The 1-foot burner is more economical when in the best condition, but requires a higher gas pressure, and is rather too powerful a unit light for good illuminating effect; the 0.5 burner naturally gives a better illuminating effect, but its economy is surpassed by the 0.7-foot burner, which is not too powerful for the human eye.
For convenience of comparison, the illuminating powers and duties of the 0.5- and 0.7-foot acetylene burners may be given in different ways:
ILLUMINATING POWER OF SELF-LUMINOUS ACETYLENE.
0.7-foot Burner. | Half-foot Burner. | 1 litre = 1.36 candles. | 1 litre = 1.27 candles. 1 cubic foot = 38.5 candles. | 1 cubic foot = 35.9 candles. 1 candle = 0.736 litre. | 1 candle = 0.79 litre. 1 candle = 0.026 cubic foot. | 1 candle = 0.028 cubic foot.
If the two streams of gas impinge at an angle of 90°, twin-injector burners for acetylene appear to work best when the gas enters them at a pressure of 2 to 2.5 inches; for a higher pressure the angle should be made a little acute. Large burners require to have a wider distance between the jets, to be supplied with acetylene at a higher pressure, and to be constructed with a smaller angle of impingement. Every burner, of whatever construction and size, must always be supplied with gas at its proper pressure; a pressure varying from time to time is fatal.
It is worth observing that although injector burners are satisfactory in practice, and are in fact almost the only jets yet found to give prolonged satisfaction, the method of injecting air below the point of combustion in a self-luminous burner is in some respects wrong in principle. If acetylene can be consumed without polymerisation in burners of the simple fish-tail or bat's-wing type, it should show a higher illuminating efficiency. In 1902 Javal stated that it was possible to burn thoroughly purified acetylene in twin non-injector burners, provided the two jets, made of steatite as usual, were arranged horizontally instead of obliquely, the two streams of gas then meeting at an angle of 180°, so as to yield an almost circular flame. According to Javal, whereas carbonaceous growths were always produced in non-injector acetylene burners with either oblique or horizontal jets, in the former case the growths eventually distorted the gas orifices, but in the latter the carbon was deposited in the form of a tube, and fell off from the burner by its own weight directly it had grown to a length of 1.2 or 1.5 millimetres, leaving the jets perfectly clear and smooth. Javal has had such a burner running for 10 or 12 hours per day for a total of 2071 hours; it did not need cleaning out on any occasion, and its consumption at the end of the period was the same as at first. He found that it was necessary that the tips should be of steatite, and not of metal or glass; that the orifices should be drilled in a flat surface rather than at the apex of a cone, and that the acetylene should be purified to the utmost possible extent. Subsequent experience has demonstrated the possibility of constructing non-injector burners such as that shown in Fig. 13, which behave satisfactorily even though the jets are oblique. But with such burners trouble will inevitably ensue unless the gas is always purified to a high degree and is tolerably dry and well filtered. Non-injector burners should not be used unless special care is taken to insure that the installation is consistently operated in an efficient manner in these respects.
GLOBES, &C.—It does not fall within the province of the present volume to treat at length of chimneys, globes, or the various glassware which may be placed round a source of light to modify its appearance. It should be remarked, however, that obedience to two rules is necessary for complete satisfaction in all forms of artificial illumination. First, no light much stronger in intensity than a single candle ought ever to be placed in such a position in an occupied room that its direct rays can reach the eye, or the vision will be temporarily, and may be permanently, injured. Secondly, unless economy is to be wholly ignored, no coloured or tinted globe or shade should ever be put round a source of artificial light. The best material for the construction of globes is that which possesses the maximum of translucency coupled with non-transparency, i.e., a material which passes the highest proportion of the light falling upon it, and yet disperses that light in such different directions that the glowing body cannot be seen through the globe. Very roughly speaking, plain white glass, such as that of which the chimneys of oil-lamps and incandescent gas-burners are composed, is quite transparent, and therefore affords no protection to the eyesight; a protective globe should be rather of ground or opal glass, or of plain glass to which a dispersive effect has been given by forming small prisms on its inner or outer surface, or both. Such opal, ground, or dispersive shades waste much light in terms of illuminating power, but waste comparatively little in illuminating effect well designed, they may actually increase the illuminating effect in certain positions; a tinted globe, even if quite plain in figure, wastes both illuminating power and effect, and is only to be tolerated for so-believed aesthetic reasons. Naturally no globe must be of such figure, or so narrow at either orifice, as to distort the shape of the unshaded acetylene flame—it is hardly necessary to say this now, but some years ago coal-gas globes were constructed with an apparent total disregard of this fundamental point.