SS-t Prof. Marianlni's Examination of an Experime^it 



a few moments after the circuit is complete; so that to see 

 that current disappear, two conditions are necessary. The 

 first is, that the experiments may be made with a galvanometer 

 not very sensitive, that is, such as may not indicate the current 

 itself, except by one or two degrees of deviation. The second 

 is, that the two metals may be immersed in the acid whilst 

 they are still in communication with each other, exactly as 

 M. de la Rive conducts the experiment. But if use is made 

 of a galvanometer rather sensitive, such, for example, as may 

 show the current by a deviation of ten or more degrees, it is 

 very true that in a few moments the force of the current is 

 much weakened ; but it does not fail to be visible with some 

 degree of deviation, even after more than a minute ; so that 

 the deviation is strong at first, but proceeds always more slowly 

 in the times succeeding to the first immersion of the plates. 



But experimenting with the galvanometer of moderate deli- 

 cacy, if the plates are kept some little time in the liquid before 

 completing the circuit with the galvanometric wire, it is seen 

 that the current does not then cease so quickly ; and it is 

 stronger if more time is allowed to pass before closing the 

 circuit itself. 



The following are some experiments instituted already many 

 times here in Modena, and with the galvanometer sufficiently 

 sensitive, above mentioned. 



A small plate of pure gold, and one of pure platina, being 

 immersed for an instant in nitric acid, deprived entirely of 

 hydrochloric acid whilst they remained in contact by means 

 of the wire of the galvanometer, produced a deviation of 4°. 



Two other similar plates being left immersed for half a 

 minute, and then the circuit being closed for a moment, the 

 deviation was of 10°. 



The experiment being repeated with two other plates, and 

 the circuit being completed for a minute after they were im- 

 mersed, 25°. 



Being left immersed for five seconds before completing the 

 circuit, 75°. 



The two small plates were kept at the distance of a centi- 

 meter from each other, and were immersed together in the 

 liquid for a square centimeter of their surfaces. 



The nitric acid increases the relative electromotive faculty 

 of both those metals, but much more that of the platina than 

 that of the gold, and thence may be drawn easily the explana- 

 tion of these and of various other phaenomena which are ob- 

 served with the voltaic pair of platina and gold, when nitric 

 acid is made use of for a moist conductor. (See my above- 

 mentioned memoir at §§ XXV. XXVI.) 



