410 Professor Draper's Description of the Tithonometer. 



confined, is yellow commercial muriatic acid, holding such a 

 quantity of chlorine in solution that it exerts no action on the 

 mixed gases as they are produced. From the mode of its 

 preparation it always contains a certain quantity of chloride 

 of platina, which gives it a deep golden colour, a condition of 

 considerable incidental importance. 



When muriatic acid is decomposed by voltaic electricity its 

 chlorine is not evolved, but is taken up in very large quantity 

 and 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 decom- 

 posed will not yield equal measures of chlorine and hydrogen 

 unless it has been previously impregnated with a certain vo- 

 lume of the former gas. Nor is it possible to obtain that de- 

 gree of saturation by voltaic action, no matter 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 circumstances, 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 required. 



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 anti- 

 cipated. I have examined the wires of tithonometers that 

 had been in active use for four months, and could not per- 

 ceive the platina sensibly 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 man- 

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

 to the siphon a b c of the tithonometer, and its constitution 

 finally adjusted 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 di- 

 mensions, which contains nitric acid. Outside this porous 



