544 M. PoggendorfF on Galvanic Circuits composed of 



trated acid Avith 4 vol. water, or in weight 1 and 2 parts). In 

 this case there Mas no indication of s > i ; the first deflexion 

 occurred even with the first immersion of the platina in favour 

 of s <.i, and indeed very violently = 90°. All the succeeding 

 effects were likewise powerful, and in the same direction. The 

 deflexion was, with slight vibrations, 80°, 70°, 60°, and so on, 

 till at last about 20°, from whence, remarkably enough, it again 

 increased. The amplitude of the last observed vibration m ent 

 from 70° + 30°. 



The violent action of the acid on the zinc obliged me to ter- 

 minate the experiment ; but it was immediately recommenced 

 with amalgamated zinc and the same acid. At present the cur- 

 rent was nearly zero; only a slight deflexion of about 4° be- 

 trayed an inclination to 5 < z. 



I now heated the platina, and indeed only that plate wJiich 

 was to stand in the acid. On contemporaneous immersion of 

 both plates (of which the one heated had naturally, as in all 

 similar experiments, perfectly cooled) a deflexion of 90° in the 

 direction s:^i first resulted, immediately succeeded by one like- 

 wise of 90° in the direction 5 < i, and the needle now vibrated 

 on the same side of the meridian, successively about the points 

 85°, 80°, 75°, 70°, 60°, 50°, 40°, till at last, after some minutes, 

 it merely indicated a permanent deflexion of 2°, but still ahvays 

 in the direction s < i. 



The heating of the platina M^as at present performed on the 

 other plate, which was to be placed in the iodide of potassium. 

 The result on immersion was of the same kind, but considerably 

 less in strength than the previous one. The first deflexion 

 in favour of ^ > f amounted only to 5°, and the one immediately 

 succeeding, in the direction * < i, to 22° only, upon which the 

 needle then soon came to rest. A second heating of the plate 

 to be placed in the acid, produced again the same result in its 

 whole force. The first deflexion, in the direction s >- «, was 90°; 

 the second, in the direction s <.i, likewise 90°, and the current 

 now retained this direction with great energy, which diminished 

 but very sloAvly*. 



* This pliEenomenon also appeared when dilute hydrochloric acid was em- 

 ployed, and to a far greater extent. Jf, after the effect has decreased to zero, 

 the plate standing in the acid be taken out, washed, heated, and, after cooling, 

 re-immersed, a movement of 90°, in the direction s <: i, is immediately ob- 

 tained, succeeded by a highly permanent deflexion in the same direction. If 

 after the deflexion has again descended to nearly zero, we perform the same 

 operation with the plate inserted in the iodide of potassium, this has but a very 

 weak, in most cases, no result. Heating of both plates acted as when this was 

 performed solely with the first. I likewise observed on this occasion that 

 heated plates of platina almost wholly lose their remarkable effect by being 

 suspended for some hours in the atmosphere. 



