70 Dr. tlare’s Improved Kudiomeiers. 
In order to use the Eudiometer, it must be full of water, 
and free from air bubbles, and previously proved air tight,* 
the rod being introduced to its hilt, and the capillary orifice 
open, in consequence of the pressure of the finger on the 
Jever by which it is usually closed. Being thus prepared, let 
us suppose that it were desirable to analyze the atmosphere. 
Draw out the rod 200 measures; 4 bulk of air, equivalent to 
the portion of rod thus withdrawn, will of course, enter at the 
capillary opening; after which the lever must be allowed to 
close it. Introduce the recipient into a bell glass of hydro- 
gen, and opening the orifice, draw out the rod about 100 de- 
grees; close the orifice, and withdraw the instrument from 
the water. Apply the projecting wires (WW) severally to the 
solder (in the two furrows in the beam, fig. 2.) communicating 
with the poles of the four calorimotors, then raise the jug so 
as that it may receive one of them, and subject it to the acid. 
By the consequent ignition of the wire, the gas will explode. 
The instrument being plunged again into the water of the 
pneumatic cistern, so that the capillary orifice, duly opened, 
may be just below the surface; the water will enter and fill 
up the vacuity caused by the condensation of the gases. The 
residual air being excluded by the rod, the deficit will be 
equivalent in bulk, to the portion of the rod remaining with- 
out; and its ratio to the air subjected to analysis, may be 
known by inspecting the graduation. 
In the case of the gaseous mixtures above described, the 
deficit has, in my experiments, been 126 measures. Where- 
* To prepare the instrument and prove it to be in order, depress the 
‘lass receiver below the surface of the water in the pneumatic cistern, 
the capillary orifice being uppermost, and open; draw the rod out of 
its tube, and return it alternately, so that at each stroke, a portion of 
water,may pass in, and a portion of air may pass out. During this op- 
ration, the instrument should be occasionally held in such a posture, as. 
that all the air may rise into the glass recipient, without which its ex 
pulsion, by the action of the rod, is impracticable. Now close the ori- 
fice, (at the apex A,) and draw out a few inches of the rod, in order to 
see whether any air can enter at the junctures, or pass between 
the collar of leathers and the sliding rod. If the instrument be quite 
ait tight, the bubbles extricated in consequence of the vacuum pro- 
duced by withdrawing the rod will disappear, when it is restored to 
its place. This degree of tightness is easily sustained-in a well-made 
instrument. 
