438 M. Oersted on [June, 



known to several philosophers before those of M. Schweigger, 

 which circumstance has given rise to different names for the 

 same apparatus. M. Poggendorf has made a very useful appli- 

 cation of this apparatus by employing it for the purpose of exa- 

 mining the order of the conductors in the galvanic series. An 

 account of his labours, is contained in the German Journal, 

 the Isis, for the year 1821. M. Avogadro, in Italy, has used the 

 same plan, but without experimenting on so great a number 

 of different bodies, his memoir contains some other observa- 

 tions which are worthy of being known. By the indications of 

 the electromagnetic multiplier, he discovered that some metals at 

 the first moment of their immersion in concentrated nitric acid, 

 produce an effect contrary to that which is observed in a few 

 seconds afterwards ; but this alteration does not occur in dilute 

 nitric acid. The metals which have exhibited this property are 

 lead and bismuth, lead and tin, iron and bismuth, cobalt and an- 

 timony. M. Avogadro states, that the first effect which occurs 

 in a concentrated acid is similar to that which happens in a 

 diluted acid, and that it is afterwards that the contrary effect is 

 perceived. I have repeated these experiments with lead and 

 bismuth, and I have confirmed them by other means, excepting 

 only that I have always had at the end of the experiment with 

 concentrated acid, the same effect as that constantly produced 

 by the dilute acid. I have also found that the bars of lead and of 

 bismuth which have been acted upon by concentrated acid, gave 

 in repeated experiments constantly the same effects as by dilute 

 acid, unless fresh surfaces were given to them before they were 

 again immersed in the acid ; this renewal of the surfaces may 

 be effected not only by mechanical means, but also by diluted 

 nitric acid. It also frequently happened that the bars which 

 had been in diluted acid, and which had been only slightly 

 wiped, gave at first in the concentrated acid a momentary 

 deviation in the same direction as in the diluted acid, very pro- 

 bably on account of the fluid which remained on their surface ; 

 they then gave for some seconds the contrary deviation ; that 

 is to say, the same as that observed when the experiment is 

 made with bars well cleaned. At length the deviation became 

 such as it would have been, if diluted acid had been employed as a 

 fluid conductor. It] is to be remarked that concentrated nitric 

 acid acts much more strongly upon bismuth than upon lead ; 

 and, on the contrary, that the diluted acid acts strongly upon 

 the lead, and scarcely at all upon the bismuth. Thus it follows, 

 that the lead acts as$the more positive metal in the dilute acid, 

 but as the negative in the concentrated acid. 



It remains only to explain why the deviation produced by the 

 concentrated acid does not continue the same during the whole 

 of the experiment. As I am travelling, I have not time to treat 

 of this, or the analogous experiments related by M. Avogadro 

 thoroughly, but I shall content myself with having contributed 



