228 Prof. Draper's Description of the Tithonometer. 



The force of this battery is abundantly sufficient both for pre- 

 paring the fluid originally, and for carrying on the tithonometric 

 operations ; it can decompose muriatic acid with rapidity, and 

 will last with ordinary care for a long time. 



Before passing to the mode of using the tithonometer, it is ab- 

 solutely necessary to understand certain theoretical conditions of 

 its equilibrium ; to these in the next place I shall revert. 



Theoretical Conditions of Equilibrium. — The tithonometer 

 depends for its sensitiveness on the exact proportion of the mixed 

 gases. If either one or the other is in excess, a great diminution 

 of delicacy is the result. The comparison of its indications at 

 different times depends on the certainty of evolving the gases in 

 exact, or at all events, known proportions. 



Whatever, therefore, affects the constitution of the sentient 

 gases, alters at the same time their indications. Between those 

 gases and the fluid which confines them certain relations subsist, 

 the nature of which can be easily traced. Thus, if we had 

 equal measures of chlorine and hydrogen, and the liquid not sat- 

 urated with the former, it would be impossible to keep them 

 without change, for by degrees a portion of chlorine would be 

 dissolved, and an excess of hydrogen remain ; or, if the liquid 

 was overcharged with chlorine, an excess of that gas would ac- 

 cumulate in the sentient tube. 



It is absolutely necessary, therefore, that there should be an 

 equilibrium between the gaseous mixture and the confining fluid. 



As has been said, when muriatic acid is decomposed by a vol- 

 taic current, all the chlorine is absorbed by the liquid and accu- 

 mulates therein ; the hydrogen bubbles however as they rise 

 withdraw a certain proportion, and hence pure hydrogen passed 

 up through the tithonometric fluid becomes exceedingly sensitive 

 to the light. 



There are certain circumstances connected with the constitu- 

 tion and use of the tithonometer which continually tend to change 

 the nature of its liquid. The platina wires immersed in it by 

 slow degrees give rise to a chloride of platina. It is true that 

 this takes place very gradually, and by far the most formidable 

 difficulty arises from a direct exhalation of chlorine from the 

 narrow tube ef; for each time that the liquid descends, a volume 

 of air is introduced, which receives a certain amount of chlorine, 



