40 



ON AN EXPLANATION OF THE ACTION OF A MAGNET ON 

 CHEMICAL ACTION 1 



BY HENRY A. ROWLAND AND Louis BELL 



[American Journal of Science [3], XXXVI, 39-47, 1888; Philosophical Magazine [5]. 



XXVI, 105-114, 1888] 



In the year 1881 Prof. Eemsen discovered that magnetism had a 

 very remarkable action on the deposition of copper from one of its solu- 

 tions on an iron plate, and he published an account in the American 

 Chemical Journal for the year 1881. There were two distinct phe- 

 nomena then described, the deposit of the copper in lines approximat- 

 ing to the equipotential lines of the magnet, and the protection of the 

 iron from chemical action in lines around the edge of the poles. It 

 seemed probable that the first effect was due to currents in the liquid 

 produced by the action of the magnet on the electric currents set up 

 in the liquid by the deposited copper in contact with the iron plate. 

 The theory of the second kind of action was given by one of us, the 

 action being ascribed to the actual attraction of the magnet for the 

 iron and not to the magnetic state of the latter. It is well known 

 since the time of Faraday that a particle of magnetic material in a 

 magnetic field tends to pass from the weaker to the stronger portions 

 of the field, and this is expressed mathematically by stating that the 

 force acting on the particle in any direction is proportional to the rate 

 of variation of the square of the magnetic force in that direction. 

 This rate of variation is greatest near the edges and points of a mag- 

 netic pole, and more work will be required to tear away a particle of 

 iron or steel from such an edge or point than from a hollow. This 

 follows whether the tearing away is done mechanically or chemically. 

 Hence the points and edges of a magnetic pole, either of a permanent 

 or induced magnet, are protected from chemical action. 



One of Prof. Remsen's experiments illustrates this most beautifully. 

 He places pieces of iron wire in a strong magnetic field, with their 

 axes along the lines of force. On attacking them with dilute nitric 

 acid they are eaten away until they assume an hour-glass form, and are 



1 Read at the Manchester meeting of the British Association, September, 1887. 



