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 decom uriatic acid with rapidity, —_ 
will last with ordinary care for a long time. 
Before passing to the mode of using the tithonometer, it is abi 
its equim) to these in the next p i > I shall revert. 
Theoriticat Conditions of Equilibrium - <The tithonometi : 
depends for its sensitiveness on the exact proportion of 
gases. If either oneor the other is in excess, a great ‘diminution i 
of delicacy is the result. ‘The’ comparison: of its indications: 
different times depends on the certainty of evolving the gases in 
exact, or at all events, known proportions. 
Whatever, therefore, Bifécts 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. E 
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 toa 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, 4 
