tjcpennicntmg on Gases, hy means of Bent Tubes. 55 
A bent tube of the form described, may be also used for dis- 
covering the quantity of gas absorbed by a liquid. For example, 
the quantity of oxygen absorbed from atmospheric air by a so- 
lution of the protosulphate of iron. The air being confined in 
the sealed branch, by the solution contained in the open one, 
will be exposed to the pressure of the column of liquid, and as 
the open end may be corked, the solution can absorb no other gas 
but that contained in the tube. The quantity absorbed may 
be known by tying, at the commencement of the experiment, a 
waxed thread around the tube, at the boundary of the air and 
liquid. 
Other gases may be absorbed by other liquids, in nearly the 
same manner ; for instance, carbonic acid by milk of lime ; only 
when any other gas than atmospheric air is introduced into the 
tube, the whole tube must be previously filled with water. The 
water in the open branch, with the exception of a small quantity 
sufficient to confine the gas, is then to be sucked out with a straw 
or small glass tube, and the milk of lime substituted for it. 
A bent tube of a small size answers best for collecting gas ; 
and one of a larger size for the absorption of gases. 
If the experiment to be performed requires any considerable 
time, the curvature of the tube may be passed through a slit 
made in a thin board, the slit being of such length that the 
branches of the tube may rest upon the board at the extremities 
of the slit. Experiments may be going on, at the same time, in 
several tubes, placed in as many slits in the same board, which 
may be made to form part of a very convenient portable frame, 
for holding a number both of bent tubes for gases, and test tubes 
for precipitations. 
Fig. 4. is the plan of a board which may be made of maho- 
gony, 8 inches square, and J of an inch thick. In it there are 
eight slits for bent tubes, and at one end it is pierced with eight 
holes for test tubes. This board forms the top of the frame. 
Another board of the same dimensions, parallel to the former, 
forms the sole; and these two boards are connected together, at 
the corners, by four small wooden pillars. The whole frame 
need not weigh more than eleven ounces. It may be placed on 
a table or shelf, and may be lifted from one place to another, 
loaded with all the tubes that it is intended to contain, without 
disturbing any of the processes going on in these. 
