Part 2
[Ill.u.s.tration: FIG. 7.--LEONI'S FLAT-FLAME BURNER.]
Two varieties of each cla.s.s 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 bra.s.s body, which fitted on to the iron stem. Between the bra.s.s 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 011 inch; but from the same burner, when the layer of wool was removed, the gas issued at a pressure of only 007 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.
BRoNNER'S BURNERS.
The credit of having produced the first flat-flame burners designed upon scientifically correct principles belongs undoubtedly to Herr Julius Bronner, 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 Bronner 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 pa.s.sing the diminishing arrangement, and come to a state of comparative rest before issuing into the atmosphere. Both these errors were successfully avoided in Bronner'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.
[Ill.u.s.tration: A TOP.
B TOP.
FIG. 8.--BRoNNER'S BURNERS.]
[Sidenote: Construction of Bronner's burners.]
The general appearance of Bronner's burner is pear-shaped; and in size it is considerably larger than an ordinary burner designed to pa.s.s an equal quant.i.ty of gas. It consists of a cylindrical bra.s.s body surmounted by a steat.i.te top, and tapering to a very small diameter at its lower end, or inlet; the latter being closed by a plug of steat.i.te, in which is a rectangular slot, or aperture, of accurately defined dimensions. The size of this aperture determines the quant.i.ty 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 ill.u.s.trations.
[Sidenote: Properties of steat.i.te.]
The material of which the more important parts of the burner are constructed is eminently adapted for the purpose. Steat.i.te 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.
[Sidenote: Varied adaptability of the Bronner burner.]
The following tables, which are extracted from the report of the Committee of the British a.s.sociation 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 the 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 quant.i.ty 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; and _vice versa_."
[8] See _Journal of Gas Lighting_, Vol. x.x.xII., p. 423, and Vol. x.x.xVI., p. 376.
TABLE I.
-----------------------------------+-----------------------------------
AT 05-INCH
AT 10-INCH
AT 15-INCH
PRESSURE.
PRESSURE.
PRESSURE.
-------+----+-----+-------+--------+-------+----+-----+-------+-------- No.
No.
Cubic
Illumi-
Illumi-
No.
No.
Cubic
Illumi-
Illumi- of
of
Feet
nating
nating
of
of
Feet
nating
nating Burner.
Top.
per
Power.
Power
Burner.
Top.
per
Power.
Power
Hour.
per Five
Hour.
per Five
Cub. Ft.
Cub. Ft.
-------+----+-----+-------+--------+-------+----+-----+-------+-------- 2
2
120
507
2413
2
2
140
525
1875 2
3
140
664
2371
2
3
195
737
1890 2
4
--
Smokes
--
2
4
230
1033
2246 2
5
--
"
--
2
5
240
1124
2342 2
6
--
"
--
2
6
--
Smokes
-- -------+----+-----+-------+--------+-------+----+-----+-------+-------- 2-1/2
2
140
553
1975
2-1/2
2
190
830
2184 2-1/2
3
170
848
2494
2-1/2
3
230
1014
2204 2-1/2
4
203
1033
2549
2-1/2
4
270
1208
2237 2-1/2
5
--
Smokes
--
2-1/2
5
285
1429
2507 2-1/2
6
--
"
--
2-1/2
6
300
1521
2535 -------+----+-----+-------+--------+-------+----+-----+-------+-------- 3
2
145
627
2162
3
2
200
848
2120 3
3
190
866
2279
3
3
240
1134
2363 3
4
213
1124
2639
3
4
280
1484
2650 3
5
--
Smokes
--
3
5
315
1704
2720 3
6
--
"
--
3
6
325
1807
2780 -------+----+-----+-------+--------+-------+----+-----+-------+-------- 3-1/2
2
150
581
1936
3-1/2
2
212
885
2087 3-1/2
3
195
830
2128
3-1/2
3
255
1263
2476 3-1/2
4
255
1208
2368
3-1/2
4
300
1447
2612 3-1/2
5
280
1438
2568
3-1/2
5
350
1807
2581 3-1/2
6
300
1558
2597
3-1/2
6
360
1945
2701 -------+----+-----+-------+--------+-------+----+-----+-------+-------- 4
2
160
636
1987
4
2
230
977
2124 4
3
210
1069
2545
4
3
290
1383
2384 4
4
265
1337
2523
4
4
330
1706
2585 4
5
345
1761
2552
4
5
410
2157
2630 4
6
355
1807
2545
4
6
420
2240
2666 -------+----+-----+-------+--------+-------+----+-----+-------+-------- 5
2
177
738
2085
5
2
260
968
1881 5
3
230
1190
2587
5
3
330
1364
2067 5
4
330
1540
2333
5
4
400
1991
2414 5
5
410
2074
2529
5
5
500
2536
2536 5
6
430
2268
2637
5
6
530
2766
2610 -------+----+-----+-------+--------+-------+----+-----+-------+--------
TABLE II.
----+----+----------------------+---------------------+------------------
AT 05-INCH
AT 10-INCH
AT 15-INCH
PRESSURE.
PRESSURE.
PRESSURE.
+-----+-------+------+-----+-------+-------+-----+-------+------ No.
No.
Cubic
Illumi-
Illum.
Cubic
Illumi-
Illum.
Cubic
Illumi-
Illum.
of
of
Feet
nating
Power
Feet
nating
Power
Feet
nating
Power Top.
Bot-
per
Power.
per
per
Power.
per
per
Power.
per
tom.
Hour.
Five
Hour.
Five
Hour.
Five
Cub.
Cub.
Cub.
Ft.
Ft.
Ft.
----+----+-----+-------+------+-----+-------+-------+-----+-------+------ A2
1
--
--
--
15
27
90
20
40
100 "
2
16
29
91
24
52
108
31
68
110 "
2
20
39
98
29
68
117
38
94
124 A3
3
21
44
105
32
78
122
44
106
120 "
3
25
48
96
38
92
121
49
122
124 "
4
25
54
108
38
96
127
52
136
131 "
4
30
64
107
45
108
120
59
148
125 "
5
32
77
20
51
132
130
68
180
132 "
6
37
87
118
58
155
133
77
210
136 "
7
35
86
123
59
160
136
84
230
137 "
8
37
90
122
62
168
135
86
234
136 B1
1
--
--
--
13
23
88
18
35
97 B2
2
13
23
88
21
44
105
28
64
114 "
2
16
30
94
25
60
120
34
84
124 B3
3
20
38
90
30
72
120
41
101
123 "
3
23
43
93
34
77
113
45
110
122 B4
4
23
47
02
36
88
122
50
130
130 "
4
27
59
109
43
104
121
56
150
134 B5
5
31
70
113
49
129
132
65
180
138 B6
6
38
96
126
59
164
138
80
230
144 B7
7
40
102
128
66
190
144
90
260
144 B8
8
47
118
126
73
220
151
96
300
157 ----+----+-----+-------+------+-----+-------+-------+-----+-------+------
[Sidenote: Pressure of gas with the Bronner burner.]
Doubtless the chief cause of the remarkable efficiency of the Bronner over previous burners is to be found in the pressure at which the 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 Bronner, 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 005 inch; and with an initial pressure of 05 inch, the outlet pressure was only 003 inch. On the other hand, a No. 4 steat.i.te flat-flame burner, without any arrangement for r.e.t.a.r.ding the flow of the gas, under the same initial pressure gave at the outlet 016 inch and 005 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.
[Sidenote: 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 sh.e.l.l 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 pa.s.sage of the gas, or the friction which it encounters, increases with the depth of the slit, the gas pa.s.ses 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 circ.u.mstances, 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 pa.s.sage 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.
[Ill.u.s.tration: FIG. 9.--ORIGINAL HOLLOW-TOP BURNER.
(From Wadsworth's Specification.)]
[Sidenote: Who invented the hollow-top burner.]
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 ill.u.s.trations, copied from the drawings in the specification. But 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 bra.s.s.
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.
[Sidenote: Sugg's hollow-top burner.]
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 steat.i.te 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 steat.i.te 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. Another 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 bra.s.s, so placed as to be immediately under the projecting wings of the flame.
[Ill.u.s.tration: 1868 BURNER.
1874 BURNER.
TABLE-TOP BURNER.
FIG. 10.--SUGG'S HOLLOW-TOP BURNERS.]
BRAY'S BURNERS.
The burners of Messrs. George Bray and Co. have deservedly acquired a world-wide reputation, and are in extensive use wherever gas lighting is known. Their distinguishing characteristic, and that which has won for them the high repute in which they are held, is the union of cheapness with remarkable efficiency. In all the various descriptions and cla.s.ses of burners which are produced by this firm, the characteristic referred to is preserved; although it is needless to add that the different varieties are not equally efficient. Of the three forms of flat-flame burners we have been considering--batswing, union-jet, and hollow-top--the one which, more than any other, has been the speciality of the firm is the union-jet; and it is with the development of this cla.s.s of burner that the name of Bray is most intimately and honourably a.s.sociated.
[Ill.u.s.tration: UNION-JET.
HOLLOW-TOP OR SLIT-UNION.[9]
BATSWING.
FIG. 11.--BRAY'S "REGULATOR" BURNERS.]
[9] The name "slit-union," by which Mr. Bray prefers to designate this burner, he states to be derived from the resemblance of its flame to that of the union-jet burner; while it is produced by means of a slit.
[Sidenote: Bray's "regulator" burner.]
[Sidenote: Bray's "special" burner.]
The "regulator" union-jet, which was the first notable burner produced by Messrs. Bray, has received, perhaps, a wider application than any other single gas-burner. It consists of a cylindrical bra.s.s case, screwed at one end for insertion into the fittings, and at the other containing a tip of "enamel"--a material invented by Mr. Bray, and apparently of somewhat similar composition to the "adamas" of Mr.
Leoni--the "enamel" tip being perforated, in the usual manner, with two holes, set at an angle to each other, for the outflow of the gas.
The distinctive feature of this burner is the introduction into the lower part of the bra.s.s case of a layer, or layers, of muslin; designed to check in some degree, and to steady the current or flow of the gas through the burner. At the time of its introduction, this burner compared very favourably, as regards the results it yielded, with other burners in common use; and its fairly good performances, together with the very low price at which it can be sold, cause it still to be extensively employed wherever the attainment, from the gas consumed, of the highest obtainable results may be subordinated to cheapness, or in situations where, from delicacy of construction or from the care and attention demanded, a more efficient burner may not be so suitable. But in the matter of developing the illuminating power of the gas employed, the "regulator" is far surpa.s.sed by the more recently introduced "special" burner of the same makers.
