Dr. Hare’s improved Eudiometers. 
iS) 
o>) 
Fig. 4, 
W 
io 9] 
a rod and graduation exactly similar*, excepting its being 
shorter. (See fig. 5.) 
* Tn order to ensure accuracy in the measures of gas, made by the sub- 
sidiary eudiometer, it is necessary to attend to the following precautions. 
In the first place, the instrument must be proved air-tight, and free of 
air-bubbles, by the means prescribed already in the case of the eudiometer 
for water. (See note, page 23.) The presence of air-bubbles is always 
indicated by the extent of the vacuity which appears when the glass reci- 
pient is held uppermost, and which disappears when it is held lowermost : 
the weight of the mercury acting upon the elasticity of the tubes always 
causes a minute change; but by the smallest bubbles of air the effect is 
very much augmented. The eudiometer should be introduced into the 
vessel whence the gas is to be taken, and about ten per cent more than is 
necessary drawn in by opening the orifice and duly drawing out the rod. 
The eudiometer being lifted from the mercury with as little change of 
position as possible, the rod may be adjusted accurately to the point de- 
sired. A momentary opening of the orifice causes the excess to escape. 
The gas thus measured and included is then easily transferred to the prin- 
cipal eudiometer, by introducing the apex of the subsidiary instrument un- 
der the funnel (see F, fig. 4), opening the orifice, and forcing the sliding 
rod home. 
The 
