for eocperlmenting upon small quantities of Gases. 253 
placed on the shelf within the trough, the descending part of the 
second branch dips beneath it through one of the slits in that 
shelf, and, on the stopper D being withdrawn, the gas ascends 
from the tube into the receiver. Wine-glasses and small phials 
may be conveniently employed as receivers. If a mercurial, in- 
stead of a water, pneumatic trough be employed, the gas within 
the tube may not be able to make its escape through the de- 
scending part of the second branch, on account of the pressure 
of the mercury ; but if the upper orifice of the first branch be 
corked, the gas will be forced to pass along its proper course., 
When the experiment requires the application of heat, a pot 
filled with hot sand may be placed beneath the shelf E, the cur- 
vature of the tube being sunk in the sand. 
The descending part of the second branch should be of such 
a length as to dip beneath the surface of the liquid in a pneu- 
matic trough, and, if the whole tube be 10 or 13 inches long,, 
the length of this part should be from 2 to 2 J inches. This part 
must be shorter than the ascending part of the same branch 
for when the stopper is taken out, in order to procure gas, the 
pressure of the atmosphere becomes equal on the surfaces of the 
liquid in the first branch, and in the ascending part of the second ; 
the liquid, of course, rises to the same perpendicular height in 
both. If both parts of the second branch were equal, some of 
the liquid might pass over the second angle, and be lost in the 
pneumatic trough. The first branch should be large enough to 
hold the whole of the liquid contained in the second, so that 
when the inferior orifice of the descending part of the second 
branch is closed, there may be no danger of the accumulation of 
gas forcing a quantity of liquid out at the upper orifice of the 
tube. After the tube is made, if the first branch is found to be 
not sufficiently capacious, it may be made to hold more liquid 
by blowing out part of it into a globular form, as represented in 
the figure. 
The tube which I described in a former communication and 
the one which I have described in the present, being both bent, 
it will be necessary to give to each a distinct name. Perhaps 
the name Sealed Bent Tube may be appropriately applied to the 
first, and Open Bent Tube to the present contrivance. 
* See p. 53 of this volume. 
VOL. X. NO, 20, APRIL 1824. 
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