THE SMITHSONIAN INSTITUTION, 395 



Thus, under circumstances otherwise equal, the polarization ap- 

 jiearcd somewhat greater than when tlie trougli was filled higher, as 

 already mentioned in section 35. 



Buff also remarked that tlie maximum polarization required a con- 

 siderable time to elapse before taking place. 



For one decomposing cell formed of two zinc plates in a solution of 

 sulphate of zinc, he found the value of polarization, 



p=0.85 ; 

 in our unit 



p = 94. 

 From this result he is led to the following conclusions : 

 " I regard 7? i=: 0.85 as the electrical difference of zinc and hydro- 

 gen, or as an approximation to it. In like manner I regard tlie polari- 

 zation resistance ot the platinum plates in dilute sulphuric acid as an 

 approximate value for the electrical difference between oxygen and 

 hydrogen. By the stratuili of hydrogen at the negative platinum 

 plate, and the stratum of oxygen at the positive plate, the same 

 effect is produced as though not two platinum strips, but a strip 

 of solid hydrogen and one of solid oxygen, were placed in the acid. 

 * * * The electro-motive action developed by the immediate 

 contact of hydrogen and oxygen, or the electrical difference of these 

 substances, indicates the extreme limits of the resistance, which can 

 take place by the polarization of two metals in the decomposing cell. 

 This limit will be approached the more nearly, the more perfectly the 

 immersed ])lates can be coated with the gases, and the more perfectly 

 the immediate contact of the metallic with the liquid conductors is 

 prevented," 



In the same memoir we find other experiments proving the absence 

 of polarization in all cases, in which the deposition of the gases on 

 the electrodes is prevented, which has been previously mentioned. 

 (Section 35.) 



§ 38. Dimimition of p)olarization hy heating the liquid. — De la 

 Rive describes the following experiment in the Bihlioth. Univers., 

 Fchruary, ISST, p. 388 : In the closing arc of a battery of four ele- 

 ments, he inserted a galvanometer and a decomposing cell, composed 

 of two platinum plates, immersed in a glass of water ; the galvan- 

 ometer indicated a deflection of 12°. He then placed under the posi- 

 tive pole- plate where oxygen was developed, a large spirit-flame, so 

 that the plate began to glow, and the part immersed in the liquid 

 being gradually heated by conduction, raised it to the boiling point. 

 (The platinum plate was probably bent at right-angles.) No change 

 was perceptible in the deflection ; the same was done at the negative 

 plate, but now the needle advanced to 30°. After removing the lamp, 

 the deflection returned to 12°. 



When the water was replaced by dilute sulphuric acid, the original 

 deflection was 45° ; by heating the negative plate it rose to 80°, w'hile 

 heating the positive plate had no effect whatever. 



Hence De la Rive concludes, that heat has no influence on the pas- 



