Prof. Hare's improved Eudiometrical Apparatus, 127 



pressure of the spring, acting on the lever at L, is not coun- 

 teracted by the hand of the operator. 



Suppose that while the bulb of this instrument, filled with 

 water or mercury, is within a bell glass, containing a gas, the 

 lever be pressed towards the handle, the valve is consequently 

 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 securely included, 

 as soon as the pressure of the spring is allowed to push the 

 piston beyond the lateral aperture in the chamber, and the 

 valve into the orifice O, in the apex of the bulb. 



The gas thus included may be transferred to any vessel, in- 

 verted over mercury or water, by depressing the orifice of the 

 bulb below that of the vessel, and moving the lever L, so as 

 to open the aperture A in the chamber, and the orifice of the 

 bulb simultaneously. 



The bulk of gas, included by the volumeter, will always be 

 the same ; but the quantity will be as the density of the gas 

 into which it may be introduced. Hence in order to measure 

 a gas accurately, the liquid, whether water, or mercury, over 

 which it may be confined, should be of the same height within, 

 as without. This is especially important, in the case of mer- 

 cury, which being nearly fourteen times heavier than water, 

 affects the density of a gas materially, even when its surface 

 within the containing vessel does not deviate sensibly from 

 the level of its surface without. 



To remove this source of inaccuracy, I employ a small' sy- 

 phon gauge which communicates through a cock, in the neck 

 of the bell, with the gas within. In this gauge any light liquid 

 will answer, which is not absorbent of the gas. In the case of 

 ammonia, liquid ammonia may be used ; in the case of muriatic 

 gas, the liquid acid. 



The density of the gas will be in equilibria with that of the 

 air, when the bell is supported at such a height as to cause 

 the liquid in each tube of the gauge to be in the same level. 



II. Simple Valve Volumeter, 

 Besides the lower orifice O, by which it is filled with gas, 

 the volumeter which the next figure represents, has an orifice 

 at its apex A, closed by a valve attached to a lever. This 

 lever is subjected to a spring, so as to receive the pressure re- 

 quisite to keep the upper orifice shut, when no effort is made 

 to open it. 



When this volumeter is plunged below the surface of the 



water 



