in a Letter to Mr. Faraday. 55 



end remains passive; but as soon as the ^n wire with the 

 oxidized end is put out of contact with the bend ot the foik, 

 ks second end is also turned active. If the parts of the fork 

 risino- above the level of the acid be touched by an u'on wire, 

 «art°of which is immersed and active in the acid, no commu- 

 nication of chemical activity will take place, and both ends ot 

 the fork remain passive; but by the i^moval of the uon wire 

 (with the oxidized end) from the bend of the fork this will be 

 thrown into chemical action. ^. ^^ 



\s all the pha^nomena spoken of in the preceding lines are, 

 no^doubt, in some way or other dependent upon a peculiar 

 electrical state of the wires, I was very curious to see in what 

 manner iron would be acted upon by nitnc acid when used 

 as an electrode. For this purpose 1 made use of that form 

 nf the uile called the couronne des lasses, consistmg ot htteen 

 pairs of zinc and copper. A platina wire was connected with 

 ?what we call) the negative pole of the pile, an iron wire with 

 he positive one. The free end of the platina wire was first 

 plunged into nitric acid sp. gr. 1-35 and by the free end of 

 fhe iron wire the circuit closed. Under these circumstances 

 he iron was not in the least affected by the acid; and it re- 

 mained indifferent to the fluid not only as long as the cur- 

 rent was passing through it, but even after it had ceased to 

 perform the function of the positive e ectrode. The iron wire 

 proved, in fact, to be possessed of all the properties of what 

 we have called a passive one. If such a wire is made to 

 touch the negative electrode, it instantaneously becomes an 

 active one and a nitrate of iron is formed ; whether it be sepa- 

 rate from the positive pole or still connected with it, and the 

 nrifl be strono" or weak. 



But another phaenomenon is dependent upon the passive 

 state of the iron, which phaenomenon is in direct contradiction 

 with all the assertions hitherto made by philosophical experi- 

 menters The oxygen at the anode arismg from the decom- 

 position'of water contained in the acid, does not combnie vvith 

 the iron serving as the electrode, but is evolved at it, just in 

 he same manner as if it were platina, and to such a volume 

 as to bear the ratio of 1 : 2 to the quantity of hydrogen evolved 

 at the cathode. To obtain this result 1 made use of an acid 

 fornix ^^0 times its volume of water; I found, however 

 that an Tcid containing 400 times its volume of water s^ 

 shows the phx-nomenon in a very obvious manner. But 

 I must repeat it, the indispensable condition for causing the 

 evolution of the oxygen at the iron wire is to close the circuit 

 exactly in the same manner as above mentioned. I'or if, ea- 

 empUsratid, the circuit be closed with the negative platma 

 wire, not one single bubble of oxygen gas makes Us appear- 



