or peculiar Voltaic Condition of Iron, 33 1 



a green colour, it was found incapable of communicating the 

 prepared state to iron. A piece of iron, immersed in acid 

 thus impregnated, continued to produce a lively effervescence 

 until it was entirely destroyed. 



A piece of prepared iron was immersed in a solution of 

 nitrate of copper. No precipitate resulted, but when it was 

 touched in the solution with a piece of copper, the surface 

 became instantly covered with a thick layer of metallic copper. 



Between those states of the acid, in which it is capable and 

 incapable of preparing iron, several intermediate states inter- 

 vene, in which the preparation of it is effected with more and 

 more difficulty, and the effervescence lasts longer and longer. 

 In these intermediate stales the following remarkable pheno- 

 menon sometimes occurs : the action ceases for an instant, 

 and then recommences, and that several times in succession, 

 and with convulsive intermittences, which sometimes succeed 

 each other at intervals of -J to f of a second, sometimes with 

 an extraordinary rapidity, so that they cannot be counted. 

 When they are slow, it is easy to see that the cessation of the 

 action is propagated from one extremity of the wire to the 

 other, though a reason cannot always be assigned why it 

 ceases at one extremity rather than at the other. 



It often happens that the iron, without acting with vivacity, 

 does not cease to have a brown surface, to colour the sur- 

 rounding acid, and to give off gaseous bubbles: this slow action 

 may be arrested immediately in a singular manner, by with- 

 drawing the iron from the acid, holding it for an instant in the 

 air, and then letting it fall suddenly with a little shock. In 

 half a second afterwards it seldom fails to shine with all its 

 brilliancy. 



The same effect may be produced with greater certainty, if, 

 without withdrawing the iron from the acid, it be touched with 

 a thin plate of platina. The contact of the platina, and, under 

 certain circumstances that of silver also, exercises an inverse 

 influence to that of zinc, &c. &c, in the production of the 

 prepared state, or in its preservation when it exists. Thus, 

 when operating in a capsule of platina, or upon a plate of that 

 metal placed at the bottom of a porcelain capsule, the pre- 

 paration of iron may be effected, not only with concentrated 

 acid, but with dilute acid, even when diluted with an equal 

 quantity of water. With a larger proportion of water the 

 preparation of the iron is no longer possible, even when there 

 is an intimate contact of the platina; but if a portion of acid 

 be added, the iron resumes its brilliancy and becomes pre- 

 pared. 



Once prepared, the iron resists perfectly the action of an 



2 U2 



