Dr. Beetz on the Electromotive Force of Gases. 95 



premature. He would only have been correct, provided, in 

 the gas batteries, the metallic plates were so completely coated 

 with the gases that they only acted as conductors, and did not 

 come into immediate contact with the liquid. This is, how- 

 ever, evidently not the case ; on the other hand, we always 

 observe the simultaneous action of the metal forming the basis 

 of the battery ; a phaenomenon which is evident when the gas 

 does not come into contact with the plate itself, but is only 

 slightly dissolved by the liquid ; whilst, when the gas comes 

 into immediate contact, /. e, at the point of contact of the 

 metal, the gas and the liquid, the action of the gas is at its 

 maximum, and the values then obtained are those given above. 

 I cannot therefore entirely agree with one statement made by 

 M. Buff"*, viz. " that the same effect is produced by the layer 

 of hydrogen at the negative plate of platinum (on polarization), 

 as also by the layer of oxygen at the positive plate of platinum, 

 as when, instead of two strips of platinum, a strip of solid hy- 

 drogen and a strip of solid oxygen had been introduced into 

 the acid;" but I entirely agree with the following remark on this 

 point: — " The electromotive action excited by the immediate 

 contact of hydrogen and oxygen, or the electric difference of 

 the two matters, denotes the extremelimit of the resistance (of 

 the counter force) which can possibly be produced by the pola- 

 rization of two metals in decomposing ceils. This limit is more 

 approximated in proportion to the power possessed by the im- 

 mersed plates to become coated with the gases, and to the com- 

 pleteness with which the direct contact of the metallic with the 

 liquid conductor is by this means avoided. If the partly im- 

 mersed strips could be completely isolated from the liquid by 

 the gases with which they become coated, the chemical nature 

 of the metallic masses would be a matter of perfect indiffer- 

 ence." But since the metals are not all equivalent when the 

 polarization is at its maximum, it can never be admitted that 

 the plates are completely coated with the gas, nor can the po- 

 larizing values be regarded as the true electromotive forces of 

 the gases concerned. 



Here, I think, is to be sought for the cause of the phaeno- 

 menon, that plates of the same metal yield a far greater elec- 

 tromotive force when they are coated with the gases by polari- 

 zation than when this is produced by any other means ; they 

 are coated much more perfectly by polarization. The elec- 

 tromotive force thus produced in M. Poggendorff''st experi- 

 ments, when reduced to my unit, would be 55 for polished 



* Loc. cit t PoggendorlTs Annalen, vol. Ixx. p. 179-189, 



