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.
Duplex Burner
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.
Scholl's Platinum Light Perfecter
Fig. 6.—Scholl's Platinum Light Perfecter.
Scholl's "Platinum Light Perfecter."An ingenious device for improving the efficiency of union-jet burners was brought out some twenty years ago by a Mr. Scholl, of London, and known as Scholl's "Platinum Light Perfecter," which is shown in the accompanying illustration. It consisted of a little brass ring, carrying a plate of platinum about 0·4 inch long by 0·15 inch wide. The ring fitted on to the top of the burner in such a manner that the platinum plate was held, in a vertical position, between the two orifices from which the gas emerged. The jets of gas, instead of impinging upon each other, impinged against the plate, and united above to form the flame. By the interposition of the metal plate, the velocity of the gas was much reduced; and a thicker and more sluggish flame was produced, with the result of increasing its illuminating power. When the apparatus was used upon a burner having very small orifices, and delivering its gas at a high pressure, the increase of light obtained was very striking; but with lower pressures the advantage derived from its use was correspondingly diminished. This is very clearly shown by the following table, which is extracted from a report, by Captain Webber and Mr. Rowden, on experiments upon gas-burners, carried out at the Paris Universal Exhibition, 1867.[4]
Burners were also made with the metal plate forming part of the burner head; and, instead of being of platinum, it was sometimes formed of thin steel, or other commoner metal. Where platinum was used, some advantage probably accrued from its becoming incandescent; but, of course, any benefit arising from this source was not obtained when steel was employed. The remarks which have been made respecting the limited applicability of the double-flame burner will apply, with equal force, to the apparatus under notice. Although it effected an undoubted improvement when applied to burners ill adapted to the pressure at which the gas was supplied, equally good results could be obtained without its aid, when a burner was employed suited to the quality and pressure of the gas supplied.
Leoni's flat-flame burners.Perhaps the most efficient flat-flame burners available prior to 1867 were those made by Mr. S. Leoni, of London. One of these is shown in fig. 7. This maker produced both batswing and union-jets; various sizes being made of each burner. Besides affording fairly good results from the gas consumed, the burners were supplied at a very moderate price. Their distinguishing feature was the peculiar substance of which the burner-tips were formed. This was a material invented by Mr. Leoni, and named by him "adamas." (The precise composition of "adamas" is a trade secret; but it appears to consist of a mixture of various minerals or earths, moulded in a clayey or plastic condition, and then burnt.) Previous to his invention, the tip of the burner, or the burner head, had been made, almost exclusively, of iron or brass. There were, however, some grave defects inherent in the use of metal for this purpose. The orifices of union-jets and the slits of batswings in course of time became much obstructed by the corrosion of the metal; and the efforts made to remove the obstruction only served to destroy the burner more quickly, by increasing the size and injuring the precise shape of the apertures. The "adamas" tips, on the other hand, perfectly withstood the high temperature to which they were exposed, were quite incorrodible, and were sufficiently hard to endure a considerable degree of even rough usage. By constructing the tip of this material, the efficiency of the burner was improved in many ways. The liability of the burner to corrosion being removed, and the inconvenience due to this cause done away with, the life of the burner was prolonged, and the expense of renewal consequently reduced. But, in addition to these advantages, there was yet another direction in which the "adamas" tip contributed to enhance the utility of the burner. This was in maintaining a higher temperature of the flame; and arose from its inferior capacity, compared with metal, for conducting heat from the flame. That the advantage derived from this source, although unimportant, was not altogether imaginary, will be apparent when it is mentioned that metal burners, when in operation, usually attain to a temperature of from 400° to 500° Fahr.—an indication of the amount of heat being continuously abstracted from the flame. The adoption of a non-conducting material for the burner-tip, while it did not entirely prevent, considerably reduced the loss of heat.
Leoni's Flat-Flame Burner
Fig. 7.—Leoni's Flat-Flame Burner.
Two varieties of each class of burner were made by Mr. Leoni. In the one burner, the "adamas" tip was inserted into an iron stem; in the other, the tip was inserted in a brass body, which fitted on to the iron stem. Between the brass body and the iron stem of the latter burner there was affixed a layer of wool, designed to check the pressure at which the gas was supplied. Owing, very probably, to the unsuitability of the material (wool) used for this purpose, the result was not satisfactory; as, according to the statements of Messrs. Webber and Rowden, in the report previously cited, no difference could be detected, in many experiments, between the results yielded by the burner with or without the layer of wool. Some light is shed upon this apparent anomaly by certain experiments made by the writer to determine the pressure at which gas issues from various burners. With one of Leoni's No. 4 union-jets, under an initial pressure of 1 inch (the pressure at the inlet when the burner is in operation), the pressure at the outlet of the burner, when the layer of wool was employed, was 0·11 inch; but from the same burner, when the layer of wool was removed, the gas issued at a pressure of only 0·07 inch. Thus the effect of inserting the layer of wool in the burner was exactly the opposite of that which it was intended to produce; the pressure of the issuing gas stream being increased instead of diminished.
BRÖNNER'S BURNERS.
The credit of having produced the first flat-flame burners designed upon scientifically correct principles belongs undoubtedly to Herr Julius Brönner, of Frankfort-on-the-Maine. Long before the date of his invention, efforts had been made to reduce the pressure of the gas within the burner. But these endeavours were carried out in so hap-hazard a fashion as to lead to the belief that no definite conception was entertained as to what was really required. As we have seen, layers of wool had been employed; but the area of the interstices, or the gas-way through the material, was a matter of the merest accident. And there was not the slightest guarantee that the same conditions should prevail in any two burners. Herr Brönner shrewdly detected the cause of former failures, as he clearly perceived the end which it was requisite to attain, and towards which previous inventors had been but blindly groping. Having formed a right estimate of the requirements to be fulfilled, and the difficulties to be surmounted, he set about accomplishing the desired result by other means. There were two causes which had chiefly contributed to the unsuccessful issues of previous attempts. One was the uncertain and indefinite operation of the means employed for diminishing the pressure; the other was the inadequate provision for enabling the gas to lose the current, or swirl, acquired in passing the diminishing arrangement, and come to a state of comparative rest before issuing into the atmosphere. Both these errors were successfully avoided in Brönner's invention—the former by making the inlet to the burner of restricted and definite dimensions, and of less area than the outlet, or slit; the latter by enlarging the chamber, or place of expansion within the burner, as well as by the different arrangement adopted for diminishing the pressure.
Brönner's Burners
A Top.B Top.Fig. 8.—Brönner's Burners.
The general appearance of Brönner's burner is pear-shaped; and in size it is considerably larger than an ordinary burner designed to pass an equal quantity of gas. It consists of a cylindrical brass body surmounted by a steatite top, and tapering to a very small diameter atConstruction of Brönner's burners.its lower end, or inlet; the latter being closed by a plug of steatite, in which is a rectangular slot, or aperture, of accurately defined dimensions. The size of this aperture determines the quantity of gas which, at any particular pressure, is admitted to the burner; and the slit, or outlet of the burner, being of greater area than the inlet, ensures the gas being delivered from the burner at a lower pressure than that at which it enters it. By varying the respective dimensions of these two openings, and their relation to each other, the burner may be regulated to deliver its gas at any required pressure short of the initial pressure at the entrance to the burner. The enlargement of the cylindrical body provides an expansion chamber, wherein the velocity of the stream of gas which rushes through the narrow opening at the inlet of the burner is checked, and any agitation or unsteadiness which may have been imparted to it is subdued before the gas issues into the atmosphere and is consumed. There are two kinds of tops for the burners, which are distinguished by the letters A and B. The B top is of the ordinary semi-spherical type, giving a true batswing-shaped flame; the A top is flatter, almost square in form, and yields a flame taller than, but not so broad as the former. In consequence of this difference in the shape of its flame, the latter burner is better adapted for use in globes. The general appearance of the burners, and their distinguishing peculiarities, will be clearly understood from the illustrations.
Properties of steatite.The material of which the more important parts of the burner are constructed is eminently adapted for the purpose. Steatite is a mineral which, as found in nature, is so soft as to be readily turned in a lathe, and shaped to any design; but when heated up to about 2000° Fahr. it becomes almost as hard and durable as flint, while perfectly retaining its form and colour. These properties peculiarly qualify it for receiving a slit or orifice, which, though of minute proportions, must be accurately formed to precise dimensions. Besides which, like "adamas," its capacity for conducting heat away from the flame is so limited that, in this respect, it has a considerable advantage over metal for the purpose of being formed into gas-burners.
The following tables, which are extracted from the report of the Committee of the British Association appointed to investigate the means for the development of light from coal gas of different qualities,[8]exhibit the very satisfactory results obtained by the use of these burners. In Table I., the gas operated upon was cannel gas (such as is generally supplied in Scotland), and possessed an illuminating power, when employed in the standard burner, of 26 candles per 5 cubic feet. Table II. contains the results of determinations with common gas (such as is used in London, and generally throughout the greater part of England); 5 cubic feet of which, in the standard burner, gave an illuminating power of 16 candles. The first and second columns of theVaried adaptability of the Brönner burner.tables refer to the different sizes of the tops and bottoms of the particular burners employed; there being in all some 16 sizes of the one, and 11 sizes of the other. These, being interchangeable, permit of a great variety of combinations; and enable a burner to be selected suited to any particular quality or pressure of gas. For as with pressure, so with illuminating power: In order to obtain the utmost lighting efficiency, different burners are required for gases differing in quality or their degree of richness. A burner which, with gas of one quality, will yield excellent results, may, under the same conditions of pressure and supply, be totally unsuited to gas of another quality. That this should be so will be evident from a consideration of what has been said as to the theory of burning gas to the best advantage; and, in brief, results from the richer gas containing in its composition a greater proportion of carbon, and so requiring an increased supply of air for its thorough combustion. This increased supply of air can only be obtained (with flat-flame burners) by causing the gas to issue into the atmosphere at a higher pressure; and so it comes about that, compared with the quantity of gas to be delivered through them, the slits of batswing and the orifices of union-jet burners must be considerably narrower when intended for cannel gas than when common gas is to be consumed. In other words, in order to develop its full illuminating power, it is essential that the pressure at which the gas issues from the burner should be proportioned to its quality. The gist of the matter is set forth in the general statement that "the poorer the quality of the gas, the lower must be the pressure at which it is consumed; andvice versâ."
Table I.
Table II.
Doubtless the chief cause of the remarkable efficiency of the Brönner over previous burners is to be found in the pressure at which thePressure of gas with the Brönner burner.gas flows from the burner and is consumed. In the course of some experiments made to determine the pressure at which gas is delivered from various burners, the writer found that from a No. 4 Brönner, with an initial pressure—i.e., the pressure at the inlet when the burner is in operation—of 1 inch, the gas issued at a pressure of only 0·05 inch; and with an initial pressure of 0·5 inch, the outlet pressure was only 0·03 inch. On the other hand, a No. 4 steatite flat-flame burner, without any arrangement for retarding the flow of the gas, under the same initial pressure gave at the outlet 0·16 inch and 0·05 inch respectively. The absence of anything within the burner to cause the gas to swirl, or to issue with an unsteady flow, must also be credited with contributing, in no slight degree, to the favourable results yielded by these burners.
THE HOLLOW-TOP BURNER.
In the hollow-top burner we have one of the most notable improvements which have been effected in flat-flame burners. A simple modification of the batswing—the earliest of flat-flame burners—it is not more complicated in its details than is that burner. Yet, simple as it is, its construction exhibits an important advance upon the original batswing. Indeed, this burner may be said to embody the only considerable improvement that has been made in the distinctive features of the batswing since the introduction of the latter burner, which, as we have seen, took place as early as the year 1816.
The hollow-top an improved batswing burner.In its outward form, the hollow-top burner differs little, if at all, from the batswing; but a slight modification which has been adopted in the arrangement of its interior has produced a very marked result in improving the shape of the flame yielded by the burner, and, to some extent, in the results, as regards illuminating power, which it is capable of affording. In this burner, as its name implies, the interior of the top or head of the burner is hollowed out, forming an enlargement of the cavity or chamber within the burner, and (what is chiefly important) making the shell of the dome-shaped burner head of equal thickness throughout. In the ordinary batswing, in consequence of the varying thickness of the burner at this part, the slit is much deeper in the middle than at any other part of its length, and gradually decreases in depth towards each end. As the resistance to the passage of the gas, or the friction which it encounters, increases with the depth of the slit, the gas passes out from the burner at the ends of the slit more readily than in the middle; producing a wide-stretching flame, of scanty height in proportion to its width. From the same cause the flame is not of equal thickness throughout; being thinner in the middle than at the ends. Moreover, the outer extremities of the flame, extending so far beyond the body of the burner, are unable to retain the form given to them by the lateral flow of the gas at the ends of the slit; the resistance, presented by the atmosphere, together with the natural tendency of the gas to ascend, causing the under portion of the flame to fold back upon itself. As one result of this combination of untoward circumstances, the flame is liable to smoke with a slight agitation of the surrounding air.
In the hollow-top burner, the slit is of equal depth throughout its length; and the resistance offered to the passage of the gas being the same in all parts of the slit, the gas flows through the middle as readily as at the ends—nay, in reality rather more so, owing to the innate ascensive power of the gas, due to its being lighter than air. The peculiar hollowing-out of the head of the burner, also, withdraws the ends of the slit out of the direct course or current of the gas through the burner; so that the tendency of the stream of gas to issue at these points, in preference to going through the middle of the slit, is further checked. The consequence is that the shape of the flame is considerably improved; it being taller, more compact, and not so broad as that of the batswing. In addition, the flame being of equal thickness throughout, its illuminating power is somewhat improved; while, from its compactness, it is better enabled to resist atmospheric influences. With this alteration in the shape of the flame all original resemblance to a batswing is entirely destroyed; but the appearance of the flame of the new burner is much more agreeable to the eye than that of the older batswing.
Original Hollow-Top Burner
Fig. 9.—Original Hollow-Top Burner.(From Wadsworth's Specification.)
As has been exemplified in so many instances in the history of invention, the hollow-top burner was not appreciated at its true value until long after it had been brought into existence. It appears to have been originally invented by Joseph and James Wadsworth, of Marple and Salford, and was patented by them in 1860. According to the specification of the inventors, the burners might be made either in solid or sheet metal, as will be seen from the accompanying illustrations, copied from the drawings in the specification. ButWho invented the hollow-top burner.there were difficulties in the way of casting the burners in solid metal which do not seem to have been surmounted; and those produced under the patent appear to have been made exclusively of sheet brass. For many years these burners were made and sold without their peculiarities attracting any marked attention; which would seem to imply that their faulty construction precluded the attainment of all the advantages afforded by the burner as we know it.
The superior results which the hollow-top burner was calculated to afford did not become fully apparent until the burner was made of non-conducting material, and greater care exercised in its construction. This appears to have been done in Germany earlier than in this country. But, in England, it was undoubtedly Mr. Sugg who first turned his attention to the improvement of the burner, and demonstrated its merits. Mr. Sugg commenced the manufacture of this burner in steatite in the year 1868; and since that time the burner has been extensively employed, and its advantages widely recognized. The superiority of hollow-top burners produced by Mr. Sugg to those previously manufactured, is chiefly the result of their being made in steatite instead of in metal. With this material, greater exactness and uniformity are obtained in the shape and dimensions of the burner than when metal is employed; besides which there is (what has been before referred to) the advantage arising from its inferior conductive capacity for heat, and its non-liability to corrosion. AnotherSugg's hollow-top burner.improvement, also due to Mr. Sugg, and which is productive of noticeable results, consists in cutting the slit of the burner with a circular saw, applied from above, so as to make the ends of the slit curved instead of horizontal; by which means the tendency of the gas to issue laterally at the ends of the slit, and form horns to the flame, is lessened. Mr. Sugg's table-top burner (which was introduced in 1880), in addition to the characteristic features of the hollow-top, has a rim-like projection from the burner, below the slit; its object being to protect the flame from the disturbing influence of the uprush of air in its immediate vicinity, and so preserve its shape unaltered, while diminishing its liability to smoke. Prior to Mr. Sugg—namely, in the early part of 1879—Mr. Bray had successfully obviated this injurious action upon the flame of the ascending current of air, by affixing to the burner two arms of brass, so placed as to be immediately under the projecting wings of the flame.
Three different burners
1868 Burner.—1874 Burner.—Table-Top Burner.Fig. 10.—Sugg's Hollow-Top Burners.