Chapter II: Flat-Flame Burners (2)

[8] See _Journal of Gas Lighting_, Vol. XXXII., p. 423,
and Vol. XXXVI., p. 376.

TABLE I.

-----------------------------------+-----------------------------------
| AT 0.5-INCH | AT 1.0-INCH | AT 1.5-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 | 1.20| 5.07 | 24.13 | 2 | 2 | 1.40| 5.25 | 18.75
2 | 3 | 1.40| 6.64 | 23.71 | 2 | 3 | 1.95| 7.37 | 18.90
2 | 4 | -- | Smokes| -- | 2 | 4 | 2.30| 10.33 | 22.46
2 | 5 | -- | " | -- | 2 | 5 | 2.40| 11.24 | 23.42
2 | 6 | -- | " | -- | 2 | 6 | -- | Smokes| --
-------+----+-----+-------+--------+-------+----+-----+-------+--------
2-1/2 | 2 | 1.40| 5.53| 19.75 | 2-1/2 | 2 | 1.90| 8.30 | 21.84
2-1/2 | 3 | 1.70| 8.48| 24.94 | 2-1/2 | 3 | 2.30| 10.14 | 22.04
2-1/2 | 4 | 2.03| 10.33| 25.49 | 2-1/2 | 4 | 2.70| 12.08 | 22.37
2-1/2 | 5 | -- | Smokes| -- | 2-1/2 | 5 | 2.85| 14.29 | 25.07
2-1/2 | 6 | -- | " | -- | 2-1/2 | 6 | 3.00| 15.21 | 25.35
-------+----+-----+-------+--------+-------+----+-----+-------+--------
3 | 2 | 1.45| 6.27| 21.62 | 3 | 2 | 2.00| 8.48 | 21.20
3 | 3 | 1.90| 8.66| 22.79 | 3 | 3 | 2.40| 11.34 | 23.63
3 | 4 | 2.13| 11.24| 26.39 | 3 | 4 | 2.80| 14.84 | 26.50
3 | 5 | -- | Smokes| -- | 3 | 5 | 3.15| 17.04 | 27.20
3 | 6 | -- | " | -- | 3 | 6 | 3.25| 18.07 | 27.80
-------+----+-----+-------+--------+-------+----+-----+-------+--------
3-1/2 | 2 | 1.50| 5.81| 19.36 | 3-1/2 | 2 | 2.12| 8.85 | 20.87
3-1/2 | 3 | 1.95| 8.30| 21.28 | 3-1/2 | 3 | 2.55| 12.63 | 24.76
3-1/2 | 4 | 2.55| 12.08| 23.68 | 3-1/2 | 4 | 3.00| 14.47 | 26.12
3-1/2 | 5 | 2.80| 14.38| 25.68 | 3-1/2 | 5 | 3.50| 18.07 | 25.81
3-1/2 | 6 | 3.00| 15.58| 25.97 | 3-1/2 | 6 | 3.60| 19.45 | 27.01
-------+----+-----+-------+--------+-------+----+-----+-------+--------
4 | 2 | 1.60| 6.36| 19.87 | 4 | 2 | 2.30| 9.77 | 21.24
4 | 3 | 2.10| 10.69| 25.45 | 4 | 3 | 2.90| 13.83 | 23.84
4 | 4 | 2.65| 13.37| 25.23 | 4 | 4 | 3.30| 17.06 | 25.85
4 | 5 | 3.45| 17.61| 25.52 | 4 | 5 | 4.10| 21.57 | 26.30
4 | 6 | 3.55| 18.07| 25.45 | 4 | 6 | 4.20| 22.40 | 26.66
-------+----+-----+-------+--------+-------+----+-----+-------+--------
5 | 2 | 1.77| 7.38| 20.85 | 5 | 2 | 2.60| 9.68 | 18.81
5 | 3 | 2.30| 11.90| 25.87 | 5 | 3 | 3.30| 13.64 | 20.67
5 | 4 | 3.30| 15.40| 23.33 | 5 | 4 | 4.00| 19.91 | 24.14
5 | 5 | 4.10| 20.74| 25.29 | 5 | 5 | 5.00| 25.36 | 25.36
5 | 6 | 4.30| 22.68| 26.37 | 5 | 6 | 5.30| 27.66 | 26.10
-------+----+-----+-------+--------+-------+----+-----+-------+--------

TABLE II.

----+----+----------------------+---------------------+------------------
| | AT 0.5-INCH | AT 1.0-INCH | AT 1.5-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 | -- | -- | -- | 1.5 | 2.7 | 9.0 | 2.0 | 4.0 | 10.0
" | 2 | 1.6 | 2.9 | 9.1 | 2.4 | 5.2 | 10.8 | 3.1 | 6.8 | 11.0
" | 21/2 | 2.0 | 3.9 | 9.8 | 2.9 | 6.8 | 11.7 | 3.8 | 9.4 | 12.4
A3 | 3 | 2.1 | 4.4 | 10.5 | 3.2 | 7.8 | 12.2 | 4.4 | 10.6 | 12.0
" | 31/2 | 2.5 | 4.8 | 9.6 | 3.8 | 9.2 | 12.1 | 4.9 | 12.2 | 12.4
" | 4 | 2.5 | 5.4 | 10.8 | 3.8 | 9.6 | 12.7 | 5.2 | 13.6 | 13.1
" | 41/2 | 3.0 | 6.4 | 10.7 | 4.5 | 10.8 | 12.0 | 5.9 | 14.8 | 12.5
" | 5 | 3.2 | 7.7 | 2.0 | 5.1 | 13.2 | 13.0 | 6.8 | 18.0 | 13.2
" | 6 | 3.7 | 8.7 | 11.8 | 5.8 | 15.5 | 13.3 | 7.7 | 21.0 | 13.6
" | 7 | 3.5 | 8.6 | 12.3 | 5.9 | 16.0 | 13.6 | 8.4 | 23.0 | 13.7
" | 8 | 3.7 | 9.0 | 12.2 | 6.2 | 16.8 | 13.5 | 8.6 | 23.4 | 13.6
B1 | 1 | -- | -- | -- | 1.3 | 2.3 | 8.8 | 1.8 | 3.5 | 9.7
B2 | 2 | 1.3 | 2.3 | 8.8 | 2.1 | 4.4 | 10.5 | 2.8 | 6.4 | 11.4
" | 21/2 | 1.6 | 3.0 | 9.4 | 2.5 | 6.0 | 12.0 | 3.4 | 8.4 | 12.4
B3 | 3 | 2.0 | 3.8 | 9.0 | 3.0 | 7.2 | 12.0 | 4.1 | 10.1 | 12.3
" | 31/2 | 2.3 | 4.3 | 9.3 | 3.4 | 7.7 | 11.3 | 4.5 | 11.0 | 12.2
B4 | 4 | 2.3 | 4.7 | 0.2 | 3.6 | 8.8 | 12.2 | 5.0 | 13.0 | 13.0
" | 41/2 | 2.7 | 5.9 | 10.9 | 4.3 | 10.4 | 12.1 | 5.6 | 15.0 | 13.4
B5 | 5 | 3.1 | 7.0 | 11.3 | 4.9 | 12.9 | 13.2 | 6.5 | 18.0 | 13.8
B6 | 6 | 3.8 | 9.6 | 12.6 | 5.9 | 16.4 | 13.8 | 8.0 | 23.0 | 14.4
B7 | 7 | 4.0 | 10.2 | 12.8 | 6.6 | 19.0 | 14.4 | 9.0 | 26.0 | 14.4
B8 | 8 | 4.7 | 11.8 | 12.6 | 7.3 | 22.0 | 15.1 | 9.6 | 30.0 | 15.7
----+----+-----+-------+------+-----+-------+-------+-----+-------+------

[Sidenote: Pressure of gas with the Broenner burner.]

Doubtless the chief cause of the remarkable efficiency of the Broenner 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 Broenner, 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.

[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 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.

[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 illustrations, 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 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.

[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 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. 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 brass, so placed as to be immediately under the projecting wings of the flame.

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 classes 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 class of burner that the name of Bray is most intimately and honourably associated.

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 brass 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 brass 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 surpassed by the more recently introduced "special" burner of the same makers.

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 Broenner'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 brass 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 quantity 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 passing 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 brass 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 Broenner'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 Analyst 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 | 0.5 | 3.50| 6.8 | 9.7 | 3 | 0.5 | 3.43| 11.3 | 16.4
3 | 1.0 | 4.80| 6.9 | 7.2 | 3 | 1.0 | 4.90| 15.6 | 15.8
3 | 1.5 | 6.20| 7.5 | 6.05 | 3 | 1.5 | 6.03| 17.6 | 14.6
4 | 0.5 | 4.65| 12.2 | 13.1 | 4 | 0.5 | 3.73| 13.3 | 17.8
4 | 1.0 | 6.67| 14.2 | 10.6 | 4 | 1.0 | 5.15| 17.4 | 16.9
4 | 1.5 | 8.16| 14.2 | 8.8 | 4 | 1.5 | 6.57| 22.4 | 17.1
5 | 0.5 | 5.72| 17.0 | 14.9 | 5 | 0.5 | 4.80| 17.6 | 18.3
5 | 1.0 | 7.97| 20.0 | 12.6 | 5 | 1.0 | 6.67| 24.4 | 18.3
5 | 1.5 | 9.73| 21.8 | 11.2 | 5 | 1.5 | 8.30| 30.0 | 18.2
6 | 0.5 | 5.90| 18.0 | 15.2 | 6 | 0.5 | 5.48| 20.1 | 18.3
6 | 1.0 | 8.35| 23.0 | 13.8 | 6 | 1.0 | 7.65| 28.4 | 18.6
6 | 1.5 |10.60| 28.0 | 13.2 | 6 | 1.5 | 9.20| 34.2 | 18.7
------+------+-----+-------+-------+------+------+-----+-------+-------

_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 | 0.5 | 4.22| 13.8 | 16.4 | 3 | 0.5 | 3.04| 10.8 | 17.8
3 | 1.0 | 6.37| 20.2 | 15.9 | 3 | 1.0 | 4.61| 16.4 | 17.6
3 | 1.5 | 8.14| 25.8 | 15.9 | 3 | 1.5 | 5.88| 19.9 | 16.9
4 | 0.5 | 4.25| 14.8 | 17.4 | 4 | 0.5 | 3.82| 14.2 | 18.6
4 | 1.0 | 5.88| 20.6 | 17.5 | 4 | 1.0 | 5.69| 20.8 | 18.3
4 | 1.5 | 7.95| 26.5 | 16.6 | 4 | 1.5 | 7.35| 25.6 | 17.5
5 | 0.5 | 5.25| 19.0 | 18.2 | 5 | 0.5 | 4.12| 15.4 | 18.7
5 | 1.0 | 8.14| 28.4 | 17.45| 5 | 1.0 | 6.37| 23.4 | 18.4
5 | 1.5 |10.20| 36.4 | 17.8 | 5 | 1.5 | 7.94| 28.5 | 18.0
6 | 0.5 | 5.67| 22.2 | 19.6 | 6 | 0.5 | 5.00| 19.6 | 19.6
6 | 1.0 | 8.60| 33.6 | 19.4 | 6 | 1.0 | 7.55| 29.0 | 19.2
6 | 1.5 |11.10| 39.5 | 17.8 | 6 | 1.5 | 9.70| 37.0 | 19.1
------+------+-----+-------+-------+------+------+-----+-------+-------

_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 | 0.5 | 4.16| 12.6 | 15.1 | 3 | 0.5 | 3.37| 12.4 | 18.4
3 | 1.0 | 5.64| 16.6 | 14.8 | 3 | 1.0 | 5.25| 20.4 | 19.4
3 | 1.5 | 7.83| 21.0 | 13.4 | 3 | 1.5 | 7.13| 24.0 | 16.8
4 | 0.5 | 4.26| 14.0 | 16.4 | 4 | 0.5 | 3.67| 13.0 | 17.7
4 | 1.0 | 6.74| 21.2 | 15.6 | 4 | 1.0 | 5.55| 20.6 | 18.6
4 | 1.5 | 7.81| 24.0 | 15.3 | 4 | 1.5 | 7.13| 26.0 | 18.2
5 | 0.5 | 4.76| 15.4 | 16.2 | 5 | 0.5 | 3.86| 14.6 | 18.9
5 | 1.0 | 6.93| 20.4 | 14.7 | 5 | 1.0 | 5.85| 22.6 | 19.4
5 | 1.5 | 8.72| 25.8 | 14.7 | 5 | 1.5 | 7.53| 28.0 | 18.6
6 | 0.5 | 6.04| 20.0 | 16.5 | 6 | 0.5 | 4.86| 19.4 | 20.0
6 | 1.0 | 8.82| 29.4 | 16.6 | 6 | 1.0 | 7.53| 31.6 | 21.0
6 | 1.5 |11.10| 31.6 | 14.2 | 6 | 1.5 | 9.60| 39.0 | 20.4
------+------+-----+-------+-------+------+------+-----+-------+-------

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 circumstance 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 deg.. In Bray's "regulator" burner, introduced in 1869, they were placed at an angle of 90 deg.; 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 deg.; 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.