Prof. Draper's Description of the Tithonometer. 227 



held in solution ; perhaps a bichloride of hydrogen results. If 

 through such a solution hydrogen gas is passed in minute bubbles, 

 it removes with it a certain proportion of the chlorine. From this 

 therefore it is plain, that muriatic acid thus decomposed will not 

 yield equal measures of chlorine and hydrogen, unless it has 

 been previously impregnated with a certain volume of the former 

 gas. Nor is it possible to obtain that degree of saturation by vol- 

 taic action, no malter how long the electrolysis is continued, if 

 the hydrogen is allowed to pass through the liquid. 



Practically, therefore, to obtain the tithonometric liquid, we 

 are obliged to decompose commercial muriatic acid in a glass 

 vessel, the positive electrodes being at the bottom of the vessel, 

 and the negative at the surface of the liquid. Under these cir- 

 cumstances, the chlorine as it is disengaged is rapidly taken up, 

 and the hydrogen being set free without its bubbles passing 

 through the mass, the impregnation is carried to the point re- 

 quired. 



Although this chlorinated muriatic acid cannot of course be 

 kept in contact with the platina wires without acting on them, 

 the action is much slower than might have been anticipated. I 

 have examined the wires of tithonometers that had been in ac- 

 tive use for four months, and could not perceive the platina sen- 

 sibly destroyed. It is well however to put a piece of platina foil 

 in the bottle in which the supply of chlorinated muriatic acid is 

 kept ; it communicates to it slowly the proper golden tint. 



The liquid, being impregnated with chlorine in this manner 

 until it exhales the odor of that gas, is to be transferred to the 

 siphon a b c of the tithonometer, and its constitution finally ad- 

 justed as hereafter shown. 



Thirdly, of the Voltaic Battery. — The battery, which will be 

 found most applicable for these purposes, consists of two Grove's 

 cells, the zinc surrounding the platina. 



The following are the dimensions of the pairs which I use. 

 The platina plate is half an inch wide and two inches long ; it 

 dips into a cylinder of porous biscuit-ware of the same dimen- 

 sions, which contains nitric acid. Outside this porous vessel is 

 the zinc, which is a cylinder one inch diameter, two inches long, 

 and two tenths thick ; it is amalgamated. The whole is con- 

 tained in a cup two inches in diameter, and two deep, which also 

 receives the dilute sulphuric acid. 



