Dr. Hare’s improved Eudiometers. 29 
with an additional collar of cork for confining oil about the 
rod where it enters the collar of leathers; otherwise, in ope- 
rating with mercury, 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 necessary 
only with respect to one of the gases. In analysing an inflam- 
mable gas by oxygen gas, or oxygen by hydrogen gas, it is only 
necessary that the quantity of the gas which is to be analysed, 
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 mer- 
curial eudiometer, be made to occupy the gauge. In analysing 
the air, or any mixture containing oxygen, the gauge is filled 
with hydrogen gas, as already stated; but, in examining in- 
flammable 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 eu- 
diometer which I have found most serviceable for experiments 
with nitric oxide gas; with the solutions of sulphurets; or 
those of sulphate, or muriate of iron, saturated with nitric 
oxide. 
The receiver (fig. 8), shaped like the small end of an egg, 
is employed in these experiments, being mounted so as to slide 
up and down upon a wire. 
This 
