TRANSACTIONS OF THE SECTIONS. 
51 
one and three eighths inches diameter, emitted a most overpowering 
sound. Length of tube produced no variation in the state of the 
flame, nor did increase of diameter over the above limits, although 
both produced of course a change of musical note ; but if the dia¬ 
meter of the tube, whether of glass or copper, was reduced to very 
nearly that of the external diameter of the burner, on approach¬ 
ing the end of the tube with the burner, the retractile flame was 
drawn forward, and, unless skilfully managed, was drawn out or 
extinguished at the moment the burner entered the tube; if, how¬ 
ever, the introduction was successfully effected, the moment the 
burner came within the tube the flame again retracted as before. 
The sound ceased at the moment that the flame was extinguished. 
The pressure of gas used in most of the experiments was that of 
the ordinary main-pipes in this city, about 1|- inch of water ; that 
of the current of air, which was produced by a good pair of double 
bellows, was equal to the pressure of a column of (2j inches of) 
mercury ; but it was found that no material alteration of effect took 
place from condensing the gas to about two atmospheres, and cau¬ 
sing it to issue inflamed at that pressure, provided the pressure of 
the current of air was likewise increased in the same ratio nearly. 
With a less powerful stream of air than was above stated, the 
effects were imperfectly produced; and with a much more powerful 
one the flame was blown out. 
The temperature of the current of air heated by the flame, when 
it retracted best, was found, at the distance of four inches from the 
burner, to be 432° Fahrenheit, or perhaps a little higher. The com¬ 
bustion of the flame in all the foregoing cases is absolutely perfect; 
its colour is a deep blue, and the volume of intensely heated air pro¬ 
pelled is very great, so that it may be rendered very useful for 
various purposes in the laboratory. It is not perfectly dry, but it 
is free from dust or smoke. 
On the Volatilization of Magnesia by Heat. By Professor Daubeny. 
According to Von Buch, carbonate of magnesia must have been 
sublimed by volcanic action, although such a phenomenon would, 
Dr. Daubeny conceived, be scarcely admitted by chemists as con¬ 
sistent with the known properties of that earth. 
A curious fact, however, confirmatory of the truth of Von Buch’s 
opinion, occurred to Professor Daubeny in Italy. He visited a lo¬ 
cality where there was an upper stratum of lava containing cavities. 
In one of these an English gentleman, resident on the spot, discovered 
a large quantity of carbonate of magnesia, and Professor Daubeny 
himself observed a minute portion of the same earth coating the 
outer surface of the lava. Here it is difficult to understand in what 
manner this substance could collect in the cavities or upon the sur¬ 
face of the rock, unless it had previously become volatilized by 
heat. 
