404 On the Blowpipe. 
rather on the surface of the oil or water than upon the valve it- 
self) drives the oil or water through the valve, and thus removes 
all obstructions to the further progress of the flame. 
In the hydraulic blowpipe the pressure of the gas on the valve 
is comparatively trifling, so that the least counter pressure is 
sufficient to close it; the mercury cannot be driven through the 
valve, which is so constructed that it cannot be moved out of its | 
vertical position, and the mercury must fall ou the centre of the 
plug, which of course is immediately closed. 
In Brookes’s blowpipe there is a great waste of gas, as the last 
portion remaining in the chamber cannot be made use of, owing 
to the condensation ceasing; whereas in the hydraulic blowpipe 
the whole is forced out by the action of the water. 
There is no occasion to fill the gas chamber with gas, as the 
water will force the whole out, be the quantity ever so small; and 
should tke pressure of the water be found too weak, it is very 
easy to fill the blowpipe five or six inches above the level of the 
division AB, fig. 1; but care must be taken before putting in 
this additional quantity to close the cock at K, otherwise the 
water entering the pipe H would be driven up into the safety- 
cistern and occasion much inconvenience. rene 
The safety appendages, if mercury be employed, must of course 
be made of iron; but those who prefer oil or water will find it 
easier to get them made of brass. 
Those who choose it may easily use a screen with this blow- 
pipe, by merely elongating the jet pipe, and they would have 
no need of any condensing syringe to be worked horizontally 
through the screen as in Brookes’s, since the whole of the gas 
would be introduced into the gas chamber before the experiments 
commenced, 
A small gauge to measure the quantity of air or gas in the 
chamber might be convenient, and could be easily formed by at- 
taching a properly graduated rod to a cork float; and if a small 
hole were made in the top of the box for the rod to pass through, 
it would of course indicate by its rise and fall the quantity of air 
or gas in the chamber. 
Should future experience confirm the opinion I have been in- 
duced to form of the safety of my appendages, we should have one 
instrument capable of producing every degree of heat from that 
requisite for roasting ores, bending glass, &c. to that necessary 
for the fusion of the most refractory bodies. 
When this instrument is to be used as a common blowpipe, 
nothing more is necessary than to unscrew the safety appen- 
dages from the pipe H, and simply to screw the jet pipe in their 
place, 
The 
