36. Improved Eudiometrical Apparatus, by Dr. Hare, 
Art. Vi.—Improved Eudiometrical Apparatus ; by Ros 
ERT Hare, M. D. Professor of Chemistry in the Univer- 
sity of Pennsylvania. 
PISTON VALVE VOLUMETER. 
f HAVE contrived some instruments for taking volumes of 
gas, at one time, precisely equal to those taken at another 
time. I call them volumeters, to avoid circumlocution. They 
are of two kinds; one calculated to be introduced into a 
bell glass, over water or mercury; the other may be fille 
throngh an orifice, as is usual in the case of filling a com- 
mon bottle over the pneumatic cistern. The following figure 
will convey a due conception of one of them, which, having 
a piston, I call the piston valve volumeter. 
. he lever L, is attached by 
a hinge to a piston p, which 
works inside of a chamber, 
=, C e rod of this piston 
y ~ extends beyond the packing 
through the axis of the bulb, 
B, to the orifice, O, in its 
apex, where it sustains a 
valve, by which this orifice 
is kept close, so long as the 
pressure of the spring, act- 
ing on the lever, at L, is 
not counteracted by the 
hand of the operator. 
Suppose that, while the 
‘bulb of this instrument, fill- 
be ith water or mercury, 
p = is within a bell glass, con- 
taining a gas, the lever be pressed towards the handle, the 
valve is drawn back so as to open the orifice of the apex of 
the bulb, and at the same time the piston descends below an 
aperture, A, in the chamber. The liquid in the bulb will 
_ now of course run out, and be replaced by gas, which is se- 
curely included, as soon as the pressure of the spring is al- 
lowed to push the piston beyond the lateral aperture in the 
chamber, and the valve into the orifice, O, in the apex of the 
“i 
