Effects due to Magnetization. 453 



ment shows that a higher electromotive force is obtained with 

 cells in which a ferrous reaction takes place than with those in 

 which a ferric reaction occurs, and this change in the character 

 of the reaction produced by the concentration probably accounts, 

 at least in part, for the increased electromotive force at the 

 point. 



D. The iron salts about the point electrode. 



The effect of artificially stirring the liquid, and the direct 

 influence of the fluid condition of the solution on the deflec- 

 tions observed, at once suggested movements of the liquid, 

 produced indirectly by the magnet. In order to locate these 

 currents, and determine their potence, a small cell was made of 

 two rectangular pieces of glass held by stout rubber bands to 

 thick rubber sides. Perforations in the sides admitted the 

 electrodes which were point and disc as before. The cell, 

 between the poles of the electromagnet, was in a strong light, 

 and the movements in the liquid were easily perceptible from 

 the displacements of suspended particles introduced for the 

 purpose. When very dilute nitric acid was placed in the cell, 

 and the magnet excited, some interesting phenomena were 

 observed. 



The liquid, at first colorless, almost immediately assumed a 

 pale brown color about the point, but nothing appeared at the 

 disc electrode. The iron salts were drawn as soon as formed 

 towards the point electrode, since here the rate of variation of 

 the square of the magnetic force is a maximum. 



As more iron was dissolved, a surface approximating to an 

 equipotential surface of the pointed pole, and enveloping the 

 colored iron salts, was observed enclosing the point, and at 

 some distance from it. The outline of the surface became 

 darker in a short time, and finally two or more dark contours, 

 separated by lighter portions and symmetrical with the outer 

 one, appeared between it and the point, indicating maxima and 

 minima of density. When the magnetic field was gradually 

 increased, this surface usually enlarged without breaking up 

 and holding the iron salts within it. On further strengthen- 

 ing the magnetic field to about 16,000 H the ridges merged 

 into one thick black envelope around the point. 



This phenomenon is best studied with but little iron salts 

 present, and by watching the point electrode with a microscope 

 while the strength of the magnetic field is increased and de- 

 creased continuously. The sections, fig. 3 (p. 449), show the 

 general form of these contours with different strengths of field. 



Upon breaking the field, everything dropped from the point 

 suddenly to the bottom of the cell, and on making the field 

 again, it required a few seconds for the salts to reappear at the 



