When by the battery we have wiend the index to its zero point, 
if the gas and liquid. are not in equilibrio, that zero is liable to a 
slight change. If there be hydrogen in excess the zero will 
rise,—if c 2, the zero will fall. 
1g what will be termed “interrupted experiments,” we 
_ must not too hastily-determine the position of the index on the 
scale at the end of atrial. It is to be remembered that the cause 
of movement over the scale arises from a condensation of muri- 
atic acid, but that condensation, though very rapid, is not instan- 
taneous. Where time is valuable, and the instrument in perfect 
equilibrium, this condensation may be instantaneously effected, 
by simply inclining the instrument so that its liquid may pass 
down to the closed end a, but not so much as to allow gas to es- 
cape into the other leg; the inclination of the two legs to each 
other makes this a very easy manipulation, and the gas thus 
brought into contact with an extensive liquid surface yields up 
its muriatic acid in a moment. 
wee 
Directions for using the Tithonometer. Preliminary adjust- 
ment.—Having transferred the liquid to the sealed end of the 
siphon, and placed the cap on the sentient extremity, the voltaic 
battery being prepared, the operator dips its polar wires into the 
cups pq, which are in connexion with the wires zy. Decompo- 
sition immediately takes place, chlorine and hydrogen rising 
through the liquid, and gradually depressing it, whilst of course 
@ corresponding elevation takes place in the other limb; this op- 
eration is continued until the liquid has risen to the zero. It 
takes but a few seconds for this to be accomplished. 
The polar wires having been disengaged, the tithonometer is 
removed opposite a window, care being taken that the light is 
not too strong. The cap is now lifted off the sentient extremity 
ad, and immediately the liquid descends. This exposure is al- 
lowed to continue, and the liquid suffered to rise as much as it 
will to the end a. And now, if the gases have been properly 
