4-8 Mr. Noad on the peculiar Voltaic Conditions 



^* = 2 m JS* I <^ r + vf/ (r) Ay \^~l!~ 



<f> r + rj, (r) A ^« y y ^ 

 A f = A § cos X A >j = A ^ cos Y A ^ = A g cos 21 



^ = I fl2 cos* X+ 6^ cos^ Y + c' cos^ ;2 i -^f 



= ^^ •x-# ^^ = «' cos2 X + b'cos^ Y+c cos- ^, 



ii q ■=. A cos («^— Z^r), this expression represents a wave of 

 light, moving with a velocity v = -r-, the length of the wave 



In my paper in the last Number, p. 492, 1. 4f,Jbr " a function 

 of those coefficients," read " a function of those constants." 



XIV. On the peculiar Voltaic Conditions of Iron and Bismuth, 

 By H. M. Noad, Esq, 



To the Editors of the London and Edinburgh Philosophical 

 Magazine. 

 Gentlemen, 

 T PERCEIVE by the last number of your Journal that I 

 -*- have been anticipated in some of the remarks I had in- 

 tended to make on the " Chemical peculiarity of Bismuth" by 

 Dr. Schoenbein. My last communication which you have re- 

 quested me to incorporate with the present related to phaeno- 

 mena observable when iron wire is exposed under certain cir- 

 cumstances to the action of diluted nitric acid sp. gr. 1*1 4* or 

 1 "2. The experiments described were these : — Dr. Schoenbein, 

 in referring to a short letter of mine in the Philosophical Maga- 

 zine of April last, (vol. x. p. 276) says, that " the facts there de- 

 scribed are quite the same as those previously described by him- 

 self in a letter to Dr. Faraday ;" but there is this difference be- 

 tween them, — the Professor's experiments were made with a 

 strong acid, mine with an acid much diluted with water ; in the 

 one case, as is now well known, the peculiar state of iron is 

 called forth by a variety of methods, by heat, by oxidation, by 

 previous immersion in very strong acid, by association with 

 platina, palladiuni, gold,&c., and, lastly, as Dr. Schcenbein has 

 shown, by association with peroxide of lead ; but in a diluted 



