196 METHODS OF CONTINUOUS AND INTERRUPTED OBSERVATION. 



wires with p q, as before. These may be called generating wires. Allow the liquid to 

 rise in b c until the third platina wire, z, which may be called the adjusting wire, is 

 covered an eighth of an inch deep. Then remove the negative wire from the cup p 

 into the cup r, and now the conditions for saturating the liquid are complete ; hydro- 

 gen escaping away from the surface of the liquid at z, and chlorine continually accu- 

 mulating and dissolving between x and d. This having been carried on for a short 

 time, the gas in a d is to be turned out by inclination, and the instrument recharged 

 That a proper quantity is evolved is easily ascertained by allowing total condensation 

 to take place, and observing that only a small bubble is left at a. 



886. It will occasionally happen in this preliminary adjustment, that an excess of 

 chlorine may arise from continuing the process too long. This is easily discovered by 

 its greenish-yellow tint, and is to be removed by inclining the instrument and turning 

 it out. . 



887. Thus adjusted, everything is ready to obtain measures of any effect, there being 

 two different methods by which this can be done: 1st, by continuous observation; 2d, 

 by interrupted observation. 



888. Of the Method of Continuous Observation. This is best described by resorting 

 to an example. Suppose, therefore, it is required to verify Table L, or, in other words, 

 to prove that the effect on the tithonometer is proportioned to its time of exposure. 



Put on the cap of the sentient tube a d, connect the polar wires with p q, and raise 

 the liquid to zero. 



Place the tithonometer so that its sentient tube will receive the rays properly. 



At a given instant, marked by a seconds watch, remove the cap A D, and the liquid 

 at once begins to descend. At the end of the first minute read off the division over 

 which it is passing. Suppose it is 7. At the end of the second do the same, it should 

 be 14 ; at the end of the third, 21, &c., &c. This may be done until the fiftieth divis- 

 ion is reached, which is the terminus of the scale. 



Recharge the tube by a momentary application of the polar wires : but it is conve- 

 nient first to remove any excess of muriatic acid gas in the sentient tube, by allowing it 

 time for condensation ; or, if that be inadmissible, by inclining a little on one side, so as 

 to give an extensive liquid contact. 



889. Of the Method of Interrupted Observation. It frequently happens that obser- 

 vations cannot be had during a continuous descent, as when changes have to be made 

 in parts of apparatus or arrangements. We have, then, to resort to interrupted obser- 

 vations. 



This method requires that the gas and liquid should be well adjusted, so that no 

 change can arise in volume when extensive contact is made by inclination. 



The tithonometer being charged, place it in a proper position. At a given instant 

 remove its cap, and the liquid descends. When the time marked by a seconds watch 

 has elapsed, drop the cap on the sentient tube. The liquid simultaneously pauses in 

 its descent, but does not entirely stop, for a little uncondensed muriatic acid still exists, 

 which is slowly disappearing in the sentient tube. Now incline the instrument for a 

 moment on one side, so that the liquid may run up to the end a, but not so much as to 



