Dr. Hare’s improved Eudiometers. 23 
are, by repose, recovering their igniting power. Or by using 
a vessel (fig. 3) large enough to receive, and containing acid 
enough to excite two of the calorimotors at once, the igniting 
power may be doubled. ‘The vessels for holding the acid are 
made of copper, covered with a cement of resin rendered 
tough by an adequate admixture of mutton suet. 
In order to use the eudiometer, it must be full of water, and 
free from air-bubbles, and previously proved air-tight*, the rod 
* To prepare the instrument and prove it to be in order, depress the 
glass 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 operation, the in- 
strument should be occasionally held in such a posture as that all the air 
may rise into the glass recipient, without which its expulsion by the action 
of the rod is impracticable. Now close the orifice (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 air-tight, the bubbles extricated in consequence 
of the vacuum produced 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. 
being 
