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 Brönner burner.] Doubtless the chief cause of the remarkable efficiency of the Brönner 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 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. [Sidenote: The hollow-top an improved batswing burner.]