DIRECTIONS FOR USING THE TITHONOMETER. 195 



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 /with a bulb ; but this 

 entails great inconvenience, as may be discovered by any one who will reflect on its 

 operation. 



880. 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. 



881. 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 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 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 mu- 

 riatic acid in a moment. 



882. Directions for using the Titlionometer. Preliminary Adjustment. Having 

 transferred the liquid to the sealed end of the siphon, and placed the cap on the sen- 

 tient extremity, the voltaic battery being prepared, the operator dips its polar wires into 

 the cups p q, which are in connexion with the wires x y. Decomposition immediate- 

 ly takes place, chlorine and hydrogen rising through the liquid, and gradually depress- 

 ing it, while, 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. 



883. 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 

 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 precision is not, how- 

 ever, obtained ; and if a bubble as large as a peppercorn be left, the operator will be 

 abundantly satisfied with the sensitiveness of his instrument. Commonly, at first, a 

 large residue of hydrogen gas, occupying, perhaps, an inch or more, will be left. It is 

 to be understood that even this large surplus will disappear in a few hours by absorb- 

 ing chlorine. But this is not to be waited for : as soon as no farther rise takes place 

 in a minute or two, the siphon is to be inclined on one side, and the residue turned out 

 into the open leg. 



884. Now, recurring to what has been said on the equilibrium, it is plain that this 

 excess of hydrogen arises from a want of chlorine in the tithonometric liquid. A proper 

 quantity must, therefore, be furnished by proceeding as follows: 



885. The sentient tube being filled with the liquid by inclination, connect the polar 



