T^o Fluids, and of Two Metals not in Contact, 543 



The first oscillation of the needle had the amplitude 80^ — 45° 

 (i. e. went from 80° on the one side of the meridian to 45° on 

 the other). The deflexions, however, decreased rapidly, and 

 when they had sunk to 12° — 0° the platina was removed. This 

 washed, dried, and again inserted, produced a current in the 

 direction 5 < «. The first deflexions were 90° — 85 ; the fol- 

 lowing, 85° — 80°; 80° — 75°, &c., till at last 6° — 3°, when 

 they were again taken out. The third, fourth, fifth, &c., im- 

 mersion gave aU of them currents in the direction 5 < i, only 

 commencing with slighter deflexions. 



At the same time two remarkable circumstances occurred 

 here. At the commencement, namely, the (distilled) zinc, as 

 is always the case when its surfaces are very bright, was but 

 very shghtly attacked by the dilute sulphuric acid, which also 

 in this case consisted of 1 vol. concentrated acid, and 9 vol. 

 water ; but the longer it remained in it the stronger the action 

 became, so that at last the disengagement of gas was very 

 Hvely. At the commencement, the vibrations of the needle, 

 although great, were nevertheless quite regular ; but in propor- 

 tion as the evolution of gas increased, sudden convulsions were 

 evident in the vibrations, which became greater and greater, and 

 at last passed into actual starts of 30, 40, 50, 60, 70, &c. de- 

 grees, and thus far exceeded the commencing deflexions which 

 even on the fourth immersion did not amount to more than 

 10°. All these starts took place in the direction s<.i. Their 

 progressive increase evidently pointed to an increasing ascend- 

 ency of the iodide of potassium over the acid. — The second 

 notable circumstance was, that with each taking out of the 

 platina, although both plates were removed at the same time, 

 a strong deflexion (of 90°) likewise in the direction s<i re- 

 sulted. This phsenomenon was especially surprising at the 

 close of the first immersions, as the needle then made but very 

 small and quite regular vibrations*. 



I now repeated the same experiment (zinc filed bright, pla- 

 tina not heated) with a stronger sulphuric acid (1 vol. concen- 



* I frequently observed similar starts, and especially when, on employing 

 ordinary zinc, I endeavoured to find out whether sulphuric acid or hydrochloric 

 acid (both of the degrees of dilution mentioned at p. 489.) would develope the 

 greater electromotive force. With silver, as negative metal, the convulsions 

 and starts of the needle were so powerful that I could not decide as to the di- 

 rection of the current. With platina these disturbances did not occur, because 

 it was first examined, and the acids did not then act so violently on the zinc. 

 With copper and tin they vanished in comparison to the force of the main eiFect ; 

 for with copper, the sulphuric acid, and with tin, the hydrochloric acid, had in the 

 highest degree the superiority. Subsequent experiments, partly with bright 

 filed distilled zinc, partly with ordinary, but amalgamated, showed me that also 

 with platina and silver the sulphuric acid has the ascendency, although in a 

 far less degree. 



