76 Dr. Hare's Improved Eudiometers. 
three tubes are partially supplied with water, as represented 
in the drawing. (W, fig. 4.) When the passage between the 
gauge and the recipicnt is open, if the pressure on the in- 
cluded air be more or less than that of the atmosphere, the 
water will rise in one of the gauge tubes, and sink in the 
other. Other liquids may be substituted for water, in the 
gau e. when desirable. 
In addition to the principal collar of leathers, and screws 
for rendering that collar compact, there is in the mercurial 
Eudiometers, a smail hollow cylinder, (a piece of a gun-bar- 
rel,) with an additional collar of cork for confining oil about 
the rod, where it enters the collar of Jeathers; otherwise in 
operating with mereury, the leathers soon become so dry as 
to permit air or mercury to pass by the rod. 
It may be proper to point out. that in operations with the 
hydro-oxygen Eudiometer, accurate measurement is necessa- 
ry, only, with respect to one of the gases. In analyzing an 
infammable gas by oxygen gas, or oxygen by hydrogen gas, 
it is only necessary that the quantity of the gas which is to 
be analyzed, and the deficit caused by the explosion, should 
be ascertained with accuracy. The other gas, which must 
be used in excess, sometimes greater, sometimes less, must, 
in using the Mercurial Eudiometer, be made to occupy the 
gauge. In analywing the air, or any mixture containing 
oxygen, the gauge is filled with hydrogen gas, as already 
stated; but, in examining inflammable gas, the atmospheric 
air may be left in the gauge, as its only active qualities are 
those of oxygen gas 
Figs. 6 and 7 represent those forms of the sliding-rod 
Eudiometer which I have found most serviceable for experi- 
ments with nitric oxide gas ; with the solutions of sulpburets ; 
or those of sulphate, or muriate of iron, saturated with nitric 
oxide. 
Fig. 6. 
