| At 0·5-Inch Pressure. | At 1·0-Inch Pressure. | At 1·5-Inch Pressure. | ||||||||
| No. of Top. | No. of Bottom. | Cubic Feet per Hour. | Illumi- nating Power. | Illum. Power per Five Cub. Ft. | Cubic Feet per Hour. | Illumi- nating Power. | Illum. Power per Five Cub. Ft. | Cubic Feet per Hour. | Illumi- nating Power. | Illum. Power per Five Cub. 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 |
| " | 2½ | 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 |
| " | 3½ | 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 |
| " | 4½ | 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 |
| " | 2½ | 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 |
| " | 3½ | 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 |
| " | 4½ | 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 |
Doubtless the chief cause of the remarkable efficiency of the Brönner over previous burners is to be found in the pressure at which the Pressure 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.
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. But Who 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.