Prof. Draper's Description of the Tithonometer. 229 



which with it is expelled the next time the battery raises the 

 column to zero; and this, going on time after time, finally im- 

 presses a marked change on the liquid. I have tried to correct 

 this in various ways, as by terminating the end/ with a bulb ; 

 but this entails great inconvenience, as may be discovered by any 

 one who will reflect on its operation. 



When by the battery we have raised 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 chlorine, the zero will fall. 



In making what will be termed "interrupted experiments," we 

 must not too hastily determine the position of the index on the 

 scale at the end of a trial. 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. 



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 p q, which are in connexion with the wires xy. Decompo- 

 sition immediately takes place, chlorine and hydrogen rising 

 through the liquid, and gradually depressing it, whilst of course 

 a 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 

 a d, 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 



