as excited hy Peroxide of head, 4^7 



which you had the kindness to have inserted in the Phi- 

 losophical Magazine, No. 59. (present volume, p. 133.) 

 To obtain with iron in the said solution results similar to 

 those mentioned in my letter, depending upon the action of 

 this metal on nitric acid, the following conditions must be ful- 

 filled. In the first and second case the oxidized iron wire 

 E F is to be replaced by a wire, whose end E is covered with 

 peroxide of lead : everything else remains the same as stated 

 in my letter. As to the third fact, C P D is to be an iron 

 wire having its end D associated with peroxide of lead ; E F 

 is to be a common iron wire. With respect to the fourth case, 

 E instead of being oxidized must be covered with peroxide of 

 lead. To obtain a result analogous to the fifth fact, the iron 

 wire C P D, its end D being associated with the substance 

 alluded to, must first be put into the vessels. Supposing D 

 to be within B, the end E of an iron wire E F is to be plunged 

 into A, and F afterwards into B. As the third case shows, 

 F will turn under these circumstances inactive. Things being 

 in this state, put the one end of a third common iron wire into 

 B, and afterwards its other end into A, and F will cease to be 

 in its peculiar condition. Now whatever the number of wires 

 similar to that E F may be, all their inactive ends being 

 within B turn active under the circumstances mentioned, 

 though they do not touch each other anywhere. Concerning 

 the sixth case, it is obtained exactly in the same manner as 

 stated in my letter, provided the oxidized end be replaced by 

 one covered with peroxide of lead. Bending up the common 

 end of the experimental wire, is, however, not required. The 

 best way of associating an iron wire with peroxide of lead is, 

 to make it the positive electrode of a couronne des tasses (con- 

 taining about a dozen of pairs of copper and zinc), and to put 

 the free end of this wire into a solution of the common acetate 

 of lead {saccharum Saturni) for about 8 or 10 minutes. By the 

 action of the pile the peroxide is deposited on the positive 

 iron wire. 



En passant, I must tell you, that many reasons lead me to 

 believe, that iron associated with this substance will form the 

 most pov^erful voltaic element known, and I am just about to 

 construct a pile of such couples. As to the chemical nature of 

 the matter producing the colours of Nobili's chromatic scale* 

 a notice of mine will shortly be published in Poggendorff"s 

 Annals, from which you will see that your idea upon the subject 

 is entirely correctt,and that consequently the view of the Italian 



* See Scientific Memoirs, parti, page 108. 



t Mr. Faraday's opinion upon this subject will be found in the present 

 Tolumc, p. 176. — Edit. 



3 I 2 



