412 Professor Draper's Description of the Tithonometer. 



tain amount of chlorine which with it is expelled the next 

 time the battery raises the column to zero; and this, going 

 on time after time, finally impresses a marked change on the 

 liquid. I have tried to correct this in various ways, as by 

 terminating the end f with a bulb; but this entails great 

 inconvenience, as may be discovered by any one who will re- 

 flect 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 con- 

 densation of muriatic acid, but that condensation, though very 

 rapid, is not instantaneous. 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 escape into the other leg ; the in- 

 clination 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 mo- 

 ment. 



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. Decomposition 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 operation 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 ex- 

 tremity a d, and immediately the liquid descends. This ex- 

 posure is allowed 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 adjusted, an entire condensation will take place, 

 the sentient tube a d filling completely. In practice this pre- 

 cision is not however obtained, and if a bubble as large as a 



