226 Prof. Schoenbein on the Voltaic Relations of 



taken up that subject again, and attempted first to ascertain 

 whether there is any voltaic relation of platina to inactive iron. 

 In contradiction to the results which you and 1 obtained some 

 time ago*, I have found by means of my galvanometer, 

 that iron being in its peculiar condition and associated with 

 platina gives rise to a sensible current if put into nitric acid, 

 be the latter ever so strong or somewhat diluted with water. 

 Making use of an acid of sp. gr. 1'4, the deviation of the 

 needle (on putting the iron and platina wires in connection 

 with the galvanometer) amounted to about 90°. I must not 

 omit to state that the current excited under the circumstances 

 mentioned is not a momentary but a continuous one, and at 

 the same time quite independent of any oxidation of the iron. 

 The direction of the current in question is such as it would 

 be if the latter metal was attacked by the acid, that is to say, 

 inactive iron is positive to platina. Another fact, as curious 

 and interesting as that just stated, is the following one. Two 

 platina wires being connected by one set of their ends with 

 the galvanometer, and by the other set with nitric acid or an 

 aqueous solution of sulphate of copper, excite a current, pro- 

 vided one of the ends (immersed in the fluid) of one of the 

 platina wires be covered with a film of peroxide of lead. The 

 current passes from the platina through the fluid to the per- 

 oxide: when the said film is so thin as to produce what are called 

 "Nobili's colours," it disappears within a very few seconds after 

 having been immersed in nitric acid, and the whole arrange- 

 ment connected with the wire of the galvanometer. From the 

 facts stated it appears, that platina is positive with regard to 

 peroxide of lead, and that the disappearance of that compound 

 is caused by a current which eliminates hydrogen at the nega- 

 tive peroxide, by which means the latter is reduced to prot- 

 oxide of lead and rendered soluble in nitric acid. In a similar 

 manner I have ascertained that the voltaic relation of inactive 

 iron to peroxide of lead is exactly the same as that of platina 

 to the said peroxide. In using peroxide of silver instead of 

 that of lead voltaic effects are produced quite^the same as those 

 which were just spoken of, that is to say, a continuous current 

 is excited, to which the peroxide acts the part of the cathode, 

 and either of the metals in question that of the anode. As 

 to the voltaic relation which one of the peroxides men- 

 tioned bears to the other, my experiments have shown that 

 peroxide of silver is always negative with regard to the per- 

 oxide of lead, be the fluid made use of nitric acid or a solution 

 of blue vitriol. Now, from all the facts above stated, I think 

 we maybe allowed to draw two important inferences : 1. That 

 peroxide of silver, peroxide of lead, platina, and inactive iron 

 » See Lond, and Edinb. Phil. M»g., vol. ix. p, 59 j vol. .x. p,S75,&c.— Eo, 



