466 M. J.-M. Gaugain on Grove's Gas Battery. 



with one of the gases and the liquid beneath. In order to 

 ascertain if this really is so, I made the following determina- 

 tions. I first measured the electromotive force of a couple in 

 which each of the platinums touched at the same time the liquid 

 and the gas, as prescribed by Mr. Grove. I then lowered the 

 platinum wires so as to immerse them completely and to keep 

 the liquid from contact with the gas ; and having again mea- 

 sured the electromotive force, I fouud that it was exactly the 

 same as before. It follows from this observation that the 

 action of the platinum only extends to the dissolved gas, and 

 that the jars containing gas have no other purpose than that of 

 keeping the solutions they cover in a state of saturation. 



I imagine, moreover, that I can explain why Mr. Grove has 

 arrived at an entirely different result. By my method of ob- 

 servation, the couple I used is only at work for a fraction of a 

 second; in so short a time the gaseous solutions surrounding 

 the platinum wires cannot be appreciably altered. This is no 

 longer the case when the current is allowed to circulate whole 

 days, as by Mr. Grove it was allowed to do : the liquid layers 

 which then surround the platinum wires are continually robbed 

 of the gas they contain, and must take fresh quantities from the 

 reservoirs above; the gases, which thus dissolve solely on the 

 upper surface of the liquid, must reach the platinum wires more 

 easily the nearer these are to the surface. 



The electromotive force of the gas- couple varies singularly 

 with the condition of the platinum wires used. According to 

 an old observation of Matteucci, the action of platinum wires is 

 increased by heating them in a spirit-lamp-flame some moments 

 before using them as electrodes. Under the most favourable 

 conditions the electromotive force of a gas-couple made with 

 unplatinized platinum wires scarcely exceeds 155. I take as 



unit the electromotive force of the couple -=p — T7v&> — tnat * s to 



say, that of a bismuth and copper thermoelectric couple, one of 

 whose junctions is at zero and the other at 100°. As I have 

 some time ago remarked, the electromotive force of the couple 



^o — i~on° vai *i es m different elements even using pure metals ; 



and therefore the numbers which I shall cite are not comparable 

 with those which M. J. Regnauld obtained when using a differ- 

 ent thermo-electric element from mine. 



I have found that the electromotive force of the gas-couple is 

 not modified when the oxygen bell-jar is replaced by one con- 

 taining carbonic acid, or even by a jar which only contains 

 boiled water. I have found that the couple formed by join- 

 ing a platinum wire plunged in a solution of oxygen, and a 



