Gas Burners Part 3

[Ill.u.s.tration: UNION-JET.

HOLLOW-TOP OR SLIT-UNION.

BATSWING.

FIG. 12.--BRAY'S "SPECIAL" BURNERS.]

Mr. Bray's series of "special" burners--embracing union-jet, hollow-top, and batswing--are constructed upon the principle of, and in form are somewhat similar to Bronner's burners, which have already been fully described. Apart from its being of greater bulk, the main divergence in the construction of the "special" burner from that of the earlier "regulator" is the introduction, into the lower part of the bra.s.s case, of a plug or washer of enamel, pierced by a small circular hole for the admission of gas into the burner; the diameter of this hole determining the quant.i.ty of gas which, at any particular pressure, is admitted into the burner. Just above the enamel washer, a layer of muslin is inserted, as in the "regulator" burner; which, in this case, is for the purpose of subduing the agitation, or swirl, acquired by the current of gas in pa.s.sing through the narrow aperture in the washer. A tip of enamel, made of the particular description (union-jet, hollow-top, or batswing) required, fitting into the upper part of the bra.s.s case, completes the burner. The objects aimed at in the "special" burner are to cause the gas to be consumed at the lowest pressure compatible with the maintenance of a firm flame, and with the least agitation, or swirl, in the current of gas as it issues from the burner. The former is attained, as in Bronner's burners, by diminishing the area of the opening admitting into the burner, without a corresponding diminution of the orifices through which the gas issues into the atmosphere; the latter, by the interposition of the layer of muslin which is immediately above the diminishing arrangement, as well as by the enlargement of the gas chamber in the upper part of the burner. The improvement thus effected in the illuminating power developed from the gas is well shown in the following tables extracted from an exhaustive series of tests of gas-burners carried out by Mr. T. Fairley, F.R.S.E., Borough a.n.a.lyst of Leeds, and embodied by him in a report presented to the Leeds Corporation. The full text of the report will be found in the _Journal of Gas Lighting_ for February 6, 1883.

_Medium Lighting Power Union-Jets._

-----------------------------------+----------------------------------- "Regulator" Burners. "Special" Burners.

------+------+-----+-------+-------+------+------+-----+-------+------- No. Pres- Cubic Illumi- Illumi- No. Pres- Cubic Illumi- Illumi- of sure Feet nating nating of sure Feet nating nating Burner in per Power Power Burner in per Power Power Inches Hour in per 5 Inches Hour in per 5 Stand. Cubic Stand. Cubic Candls. Feet. Candls. Feet.

------+------+-----+-------+-------+------+------+-----+-------+------- 3 05 350 68 97 3 05 343 113 164 3 10 480 69 72 3 10 490 156 158 3 15 620 75 605 3 15 603 176 146 4 05 465 122 131 4 05 373 133 178 4 10 667 142 106 4 10 515 174 169 4 15 816 142 88 4 15 657 224 171 5 05 572 170 149 5 05 480 176 183 5 10 797 200 126 5 10 667 244 183 5 15 973 218 112 5 15 830 300 182 6 05 590 180 152 6 05 548 201 183 6 10 835 230 138 6 10 765 284 186 6 15 1060 280 132 6 15 920 342 187 ------+------+-----+-------+-------+------+------+-----+-------+-------

_Medium Lighting Power Slit-Unions._

-----------------------------------+----------------------------------- "Regulator" Burners. "Special" Burners.

------+------+-----+-------+-------+------+------+-----+-------+------- No. Pres- Cubic Illumi- Illumi- No. Pres- Cubic Illumi- Illumi- of sure Feet nating nating of sure Feet nating nating Burner in per Power Power Burner in per Power Power Inches Hour in per 5 Inches Hour in per 5 Stand. Cubic Stand. Cubic Candls. Feet. Candls. Feet.

------+------+-----+-------+-------+------+------+-----+-------+------- 3 05 422 138 164 3 05 304 108 178 3 10 637 202 159 3 10 461 164 176 3 15 814 258 159 3 15 588 199 169 4 05 425 148 174 4 05 382 142 186 4 10 588 206 175 4 10 569 208 183 4 15 795 265 166 4 15 735 256 175 5 05 525 190 182 5 05 412 154 187 5 10 814 284 1745 5 10 637 234 184 5 15 1020 364 178 5 15 794 285 180 6 05 567 222 196 6 05 500 196 196 6 10 860 336 194 6 10 755 290 192 6 15 1110 395 178 6 15 970 370 191 ------+------+-----+-------+-------+------+------+-----+-------+-------

_Medium Lighting Power Batswings._

-----------------------------------+----------------------------------- "Regulator" Burners. "Special" Burners.

------+------+-----+-------+-------+------+------+-----+-------+------- No. Pres- Cubic Illumi- Illumi- No. Pres- Cubic Illumi- Illumi- of sure Feet nating nating of sure Feet nating nating Burner in per Power Power Burner in per Power Power Inches Hour in per 5 Inches Hour in per 5 Stand. Cubic Stand. Cubic Candls. Feet. Candls. Feet.

------+------+-----+-------+-------+------+------+-----+-------+------- 3 05 416 126 151 3 05 337 124 184 3 10 564 166 148 3 10 525 204 194 3 15 783 210 134 3 15 713 240 168 4 05 426 140 164 4 05 367 130 177 4 10 674 212 156 4 10 555 206 186 4 15 781 240 153 4 15 713 260 182 5 05 476 154 162 5 05 386 146 189 5 10 693 204 147 5 10 585 226 194 5 15 872 258 147 5 15 753 280 186 6 05 604 200 165 6 05 486 194 200 6 10 882 294 166 6 10 753 316 210 6 15 1110 316 142 6 15 960 390 204 ------+------+-----+-------+-------+------+------+-----+-------+-------

The quality of the gas operated upon averaged about 19 candles when tested with the Standard London Argand Burner.

In a former part of this treatise it was remarked that the flames produced by the modern representatives[10] of the batswing and fishtail burners have lost the original resemblance to the objects whence the names of those burners were derived; and that the two flames have gradually approached each other in shape, until, in their latest developments, they are practically identical. We have seen how that, by the invention of the hollow-top, a burner is obtained apparently, to all outward appearance, the same as the batswing, yet giving a greatly improved form of flame. We have now to learn how the fishtail, or union-jet burner has been modified so as to yield a flame closely agreeing with that produced by the improved slit burner.

[10] Although the true batswing is still in common use, I look upon the hollow-top as being its "modern representative;"

seeing that, in a great many instances, it has superseded the former burner--of which, indeed, it is only an improved form.

[Sidenote: How the union-jet burner has been improved.]

As first constructed, the union-jet burner gave a tall, narrow flame; its extremity being forked and jagged like the tail of a fish. Besides being unsightly, this form of flame was ill-adapted to develop, to anything like its full extent, the illuminating power of the gas. In order to obtain the best results, as regards illuminating power, the heat-intensity of the flame must be very high, so as to bring up the temperature of the particles of carbon liberated in the flame to the necessary degree of incandescence. To this end there must be concentration of the flame, in order to utilize to the full the heat of combustion. With the tall flame produced by the original union-jet burner there was too much exposure to the atmosphere for the flame to attain to the requisite intensity of heat; as well as considerable liability of the gas being brought too early into intimate contact with air, and so oxidized, or fully consumed, before its carbon had been raised to the temperature necessary to enable it to give out light. With the burner in its improved form the height of the flame is much curtailed, while it is broadened, and made more even and compact.

This alteration has been chiefly brought about by two modifications in the construction of the burner-tip--first, by hollowing out its flat upper surface; and, second, by altering the angle at which the two streams of gas emerge from the burner. By scooping out the central portion of the flat top of the burner, so as to form a hollow or depression where the gas emerges, the flat sheet of flame which is formed when the two streams of gas impinge upon each other obtains a broader base, and at the same time is preserved from drawing air into its midst. But the chief share of the improvement is due to the alteration in the angle formed by the two channels in the burner-tip.

It will be readily apparent that the more obtuse this angle--that is, the nearer the two streams of gas are to impinging against each other in a horizontal line--the more will the flame tend to spread out, or the lower the pressure required to obtain any desired spread of flame.

It is by taking advantage of this circ.u.mstance that Mr. Bray has been enabled to improve the union-jet burner. Twenty years ago this burner was usually made with the two channels in the burner-tip placed at an angle of about 60. In Bray's "regulator" burner, introduced in 1869, they were placed at an angle of 90; with the result of obtaining a more satisfactory flame, both as regards its appearance and illuminating power. In the "special" burner, which was not brought out till 1876, the angle is increased to 120; thus enabling the necessary spread of flame to be obtained with the gas issuing at a low pressure.

Another minor improvement in the latter burner consists in making the holes in the burner-tip elliptical instead of circular.

CHAPTER III.

ARGAND BURNERS.

[Sidenote: The premier gas-burner.]

The premier position among gas-burners undoubtedly belongs to the Argand; and it is from no unwillingness to recognize its claims, much less from ignorance of its merits, that I have left the consideration of this burner until now. It occupies this honourable position as much by virtue of the importance it has acquired through being accepted by Parliament as the test burner, and the peculiar relation in which it consequently stands to other burners, as for any marked superiority in operation. For while, in general, the Argand gives superior results to other burners, this is not always the case. There are circ.u.mstances and conditions to which the Argand is quite inapplicable, and where a simpler and less pretentious burner will give excellent results.

Indeed, some of the simple flat-flame burners which we have had under notice have now been brought to such a stage of perfection, that, when intelligently used, they not unsuccessfully rival the Argand. But it has been in the direction of demonstrating the illuminating power which it was possible to obtain from gas, and stimulating to the attainment, by other and simpler burners, of the same level of excellence, that the influence of the Argand has been most beneficial.

For, by reason of its peculiar construction, and more especially its mode of obtaining the air necessary for combustion, the Argand lends itself, more readily than any other burner, to the work of investigating and experimenting upon the conditions necessary for economical combustion, and the development of the highest illuminating power from the gas consumed. In this burner, the air supply to the flame is under complete control; and thus one of the chief elements of uncertainty and difficulty which are experienced in dealing with other burners is eliminated. The delivery of gas to different parts of the flame is also more susceptible of variation; and the results of such variation more fully exposed to observation. The consequence has been that the most remarkable advances in developing improved illuminating power from coal gas have been made with this burner. But after the possibility of obtaining an improved duty from the gas has been demonstrated by means of the Argand, and the conditions necessary for its attainment determined, equally good results have been achieved by other burners.

[Ill.u.s.tration: PLAN OF GLa.s.s-HOLDER AND BURNER TOP.

SECTION OF BURNER.

FIG. 13.--ARGAND BURNER.]

In thus showing the benefits to be derived from a more scientific mode of combustion, and leading the way to the fuller attainment, by other burners, of the illuminating power obtainable from the gas, the Argand burner has acted as a pioneer in the development of gas lighting. For, on account of its complexity, and its delicacy of construction, this burner has never been, nor, indeed, can ever hope to be generally employed. Besides the inconvenience and expense entailed by the cleaning and renewal, when broken, of the gla.s.s chimney which is indispensable to this burner, its very perfection as a burner precludes its being adopted under the conditions which appertain to the great majority of situations in which gaslight is required. For while, under the particular conditions as to pressure of gas, &c., for which it has been constructed, the Argand may give results surpa.s.sing any other burner, a very slight divergence from these conditions is productive of far more damaging results to the illuminating power of the flame than is the case with other and less efficient burners. The cause of this seeming anomaly will be apparent when we come to consider in detail the construction of the Argand, and the conditions which must be observed to ensure its satisfactory operation. For the present it will suffice merely to make mention of what appear to be well-established facts--viz., that the most perfect burners are the least adapted for use under uncertain and varying conditions; and that in proportion to the efficiency of a burner, under the conditions for which it has been constructed, is the injury to the illuminating power of its flame which is experienced when these conditions are departed from.

[Sidenote: What is an Argand burner?]

Resolved into its simplest form, the Argand burner may be said to consist of a hollow ring of metal, or other suitable material, provided with the necessary tubes or connections for communicating between its interior and the gas supply, and perforated on its upper surface with a number of holes for the emission of the gas. Through these holes the gas issues in a series of jets, which immediately coalesce to form one cylindrical sheet of flame. The burner is surmounted, and the flame enclosed, by a gla.s.s chimney, which is supported on a light gallery connected with the burner; the chimney serving the double purpose of shielding the flame from draughts, or currents of air (thus enabling the gas to burn uniformly and steadily), and of drawing upon the surface of the flame the supply of air necessary for its proper and complete combustion. For in the Argand the air supply is produced under conditions totally different from those which govern its production in all the other burners we have had under consideration. In flat-flame burners, the quant.i.ty of air supplied to the flame is determined by the pressure of the gas; or, in other words, the velocity with which it issues from the burner.

In Argand burners, on the contrary, the air supply is obtained quite independently of the pressure at which the gas issues; and the conditions most effective for the economical combustion of the gas, and the development from it of the highest illuminating power attainable, are only secured when the pressure of gas is reduced to a minimum.

It has been shown, in speaking of flat-flame burners, how the illuminating power of the flames yielded by such burners is injuriously affected by an excess of pressure in the gas, as it issues into the atmosphere, causing a too great intermingling of gas and air.

With such burners, however, some degree of pressure is needed, in order, by bringing the flame into contact with sufficient of the oxygen of the air, to promote the requisite intensity of combustion; whereas with the Argand the draught that is produced through the agency of the gla.s.s chimney enables the necessary supply of air to be obtained for the support of the flame without advent.i.tious aid from the pressure of the gas. Consequently, one of the chief objects to be aimed at in the construction of the latter burner is to so reduce the pressure of the gas within the burner that it may issue with little or no greater velocity than that due to its own specific lightness. In some of the best Argands this object is attained very successfully; and the ingenious devices which have been made use of to gain this end will be duly described in the sequel. But, in addition to causing the gas to issue from the burner at the minimum of pressure, it must be delivered evenly and equally at all parts of the ring of holes; so that there shall not be an excess of gas supplied to one portion of the flame, and an insufficiency to others. Then the area of the opening in the centre of the ring, through which the air supply is obtained to the inner surface of the flame, as well as the length and diameter of the gla.s.s chimney, must be so proportioned that the exact quant.i.ty of air needed to enable the flame to yield its maximum results shall be drawn upon it. These, and other equally essential requirements, have to be taken into consideration, and provided for, in constructing an efficient Argand burner. It is no wonder, therefore, that the development of the powers of this burner has taken up so much time and labour and inventive skill; and the remarkable degree of efficiency to which it has now been brought testifies to the thought and the accurate knowledge of the principles of combustion which have been brought to bear upon it.

[Sidenote: The earliest Argands.]

It is, however, only within comparatively recent years that its true principles of construction have been at all fully recognized, as evinced by the burners which have been produced. For a long period, Argand burners were made upon wholly empirical and arbitrary rules.

During the early years of gas lighting, the makers of gas apparatus, and such persons as professed to have a special knowledge of the production and utilization of the new illuminant, appear to have been ignorant of even the most obvious of the conditions required for the successful working of the burner. In one of the earliest works which appeared relating to gas lighting,[11] we find the Argand burner described as consisting of "two concentric tubes closed at the top with a ring having small perforations, out of which the gas can issue; thus forming small distinct streams of light." According to this description, the burner referred to cannot have been an Argand in the strictest sense of the word; but, in reality, must have consisted chiefly of a series of single jets placed in a circle, and surrounded by a gla.s.s chimney. But the great improvement in the amount of light developed, which resulted from bringing the jets of flame closer together, so as to cause them to coalesce and produce one h.o.m.ogeneous ma.s.s of flame, could not long escape notice; and accordingly we find that in "Clegg's Treatise," which appeared twenty-five years later, the proper disposition of the holes in the ring, necessary for the successful operation of the burner, is clearly recognized. In this work, speaking of the Argand burner, it is remarked (p. 193) that "the distance between the holes in the drilled ring should be so much that the jet of gas issuing from each shall, when ignited, just unite with its neighbour."

[11] Acc.u.m's "Treatise on Gas-Lights."

Before a really efficient burner could be produced, there were, however, to be successfully encountered other problems, the precise nature of which was not so clearly apparent as that of the one above referred to; otherwise their solution would not have been so long delayed. Of these, the most important, and at the same time the most difficult, were two--namely, the right adjustment of the air supply, and the most advantageous pressure at which to consume the gas. In the earliest Argands, not the slightest provision was made for diminishing the pressure of the gas before it was consumed. It was thought that everything had been accomplished that was necessary if the holes for its emission were sufficiently minute to allow of no more than the required quant.i.ty of gas pa.s.sing through them at the extreme pressure at which it was supplied to the burner. The consequence was that the gas, issuing from the burner at a very high velocity, became so intermingled with air before it was consumed, that its flame was excessively cooled; and only a small fraction of the illuminating power available was developed. Then as to the air supply. In nearly every burner produced prior to Mr. W. Sugg's invention of the "London"

Argand in 1868, this was greatly in excess of the requirements; nor is it to be wondered at. Had the supply of air been delicately adjusted, while yet there was no provision for diminishing the pressure of gas at the burner, the flame would have been liable to smoke on any sudden increase in the pressure of gas in the mains; and the annoyance and inconvenience occasioned by a smoking flame were greater drawbacks than the loss of light experienced through having the air supply greatly in excess. Thus, although during this period there were many so-called "improved" burners brought into notice, in none of them were these two cardinal requirements in the production of an efficient burner clearly recognized and seriously grappled with; and, consequently, the high level of excellence to which the Argand is capable of being brought was not attained.

SUGG'S ARGANDS.

[Sidenote: The 'London' Argand.]

The invention by Mr. W. Sugg, in 1868, of the famous "London" Argand const.i.tutes an important epoch in the history of gas lighting. Prior to that time, the construction of this cla.s.s of burners had been carried out in a wholly empirical manner; and such improvements as had been effected must be looked upon as being rather the fortuitous issues of hap-hazard endeavours, than as resulting from the acquirement of clearer views as to the conditions to be complied with in order to ensure the successful operation of the burners. The invention of the "London" Argand was the first earnest attempt to abandon the former chance methods, and to proceed upon more scientific lines. Its construction shows that its inventor possessed a thorough acquaintance with the principles of combustion; while, in many particulars, it exhibits an intelligent discernment, and a successful application of the precise means required to attain a desired end. In this burner, the extreme importance of causing the gas to issue at a low pressure is for the first time clearly recognized; and the manner in which this object is so successfully attained is as simple as it is ingenious. At the entrance to the burner the gas is divided among three narrow tubes, the combined capacity of which is much smaller than that of the pipe supplying the burner. Through these tubes the gas is conducted into a concentric cylindrical chamber (forming the main body of the burner), where its rapid flow is checked; the current, or swirl, which it may have acquired, is subdued; and the gas comes to a state of comparative rest before it issues into the atmosphere and is consumed. The top rim of this concentric cylinder is pierced with 24 holes, the aggregate area of which is considerably greater than that of the three supply-tubes; thus ensuring that the gas shall be delivered at a much lower pressure than that at which it enters the burner. By dividing the gas into three streams, which enter the cylindrical chamber at equidistant points in its circ.u.mference, the supply is equally distributed throughout the entire ring of holes; and a flame of even and regular shape is the result.

The arrangement by which, in this burner, the air supply is obtained and regulated is as noteworthy as are the means adopted for controlling the pressure of the gas. The opening within the circular ring of holes is much smaller than in previous Argands; thereby proportionately reducing the quant.i.ty of air supplied to the inner surface of the flame. The s.p.a.ce between the cylindrical body of the burner and the gla.s.s chimney is occupied by a truncated cone of thin metal, the upper edge of which is on a level with, and reaches to within a very short distance of the rim of the burner; while its base rests upon the gallery supporting the chimney. By means of this cone, all the air entering between the burner and the chimney is directed upon the immediate surface of the flame; thereby promoting intensity of combustion, and a higher illuminating power of the flame. Then the chimney itself is of such dimensions that, with the quant.i.ty of gas for which the burner has been constructed, just sufficient air is drawn upon the flame to completely consume the gas by the time the top of the chimney is reached; a flame of such length as to nearly reach to the top of the chimney, without smoking, being the most effective and economical for the quant.i.ty of gas consumed.

[Ill.u.s.tration: FIG. 14.--SUGG'S "LONDON" ARGAND.

(_Full Size._)]

Another matter which tended not a little to enhance the results yielded by this burner was an alteration in the material of which the body of the burner was constructed. In previous Argands, this had, in almost every instance, been metal; whereas in the "London" burner steat.i.te was employed. How the illuminating power of the flame is affected by the material of which the burner is constructed has been gone into so fully before (in relation to flat-flame burners), that it is unnecessary to dwell upon the matter here; only remarking that as in Argands the contact surface between the burner and the flame is relatively so much greater than in flat-flame burners, the cooling of the flame due to this cause is proportionately increased.

[Sidenote: The standard test burner.]

[Sidenote: The improved "London" Argand.]

So great was the improvement effected by this burner in the illuminating power developed from the gas consumed, so obvious its superiority to every previous Argand, that it was immediately adopted by the Metropolitan Gas Referees as the standard burner for testing ordinary coal gas within the area of their jurisdiction; and from that time down to the present it has continued to be prescribed in Acts of Parliament as the burner to be employed in testing ordinary coal gas, not only in the Metropolis, but generally throughout the United Kingdom. But although, as the standard test-burner, the original "London" Argand can still be obtained, it has been far surpa.s.sed, in the results yielded, by a new series of Argands, in which the same ingenious inventor has still further applied the principles first put into practice in the former burner. In this newer series of burners, the details of construction before adopted are modified in two or three particulars; but without departing from the general principles embodied in the arrangement of the earlier burner. Thus the holes in the ring are considerably larger, while the three supply-tubes remain of exactly the same capacity as before; by which means the gas is delivered at a much lower pressure. As the increased size of holes necessitates that the cylindrical body of the burner should be of enlarged diameter, the opening in the centre becomes of greater area than before. Were it to remain so, it would permit too large a quant.i.ty of air to be drawn upon the inner surface of the flame; to obviate which result a metal spike rises in the centre, reducing the area of the opening, and proportionately diminishing the quant.i.ty of air which would otherwise be admitted at this part of the burner. The arrangement for regulating the air supply to the outer surface of the flame is likewise modified, but in a different direction. The upper edge of the cone is brought nearer to the rim of the burner, and slightly curved, so as to direct the air more completely upon the flame; while the base of the cone, instead of extending to the gla.s.s chimney in an unbroken surface, is pierced by a number of holes, which admit air between the cone and the chimney. The action of this third current of air is to keep the chimney cool, and to steady the flame; and, in addition, it may be that it provides a supply of air to support and intensify combustion at the upper extremity of the flame.

The combined effect of these alterations is to cause the burner to develop from 7 to 12 per cent. more light from the gas consumed, than is yielded by the original "London" Argand.

[Sidenote: Silber's Argand burner.]