Effects due to Magnetization. 487 



of the dioxide showed the " protective throw " to be very 

 decided with sulphuric acid when the hydrogen is removed 

 from the surface of the electrodes in this manner. 



Gr. The Electromotive Force. 



Several attempts were made to obtain the relation between 

 the strength of field and the electromotive force developed in 

 the "protective throw"; but it was difficult to obtain con- 

 sistent readings owing to the trouble of balancing the original 

 deflexion, and the small absolute values of this electromotive 

 force when hardened gelatine was employed. 



A curve was constructed, however, showing the variation 

 of the galvanometer deflexion with the strength of field, using 

 nitric-acid solution without gelatine. This is shown in fig. 2. 



The readings were taken one after another as rapidly as 

 possible, to eliminate the damping effects of the iron salts 

 formed. 



The curve exhibits the general character of the variation. 

 In the region from about 3500 H to 8000 H the greatest rate 

 of change occurred, and beyond 10,000 H the curve became 

 nearly horizontal for the particular electrodes used. Curves 

 were also constructed for the " concentration throw " on 

 making the field under different conditions, and they were 

 approximately right lines, more or less inclined according to 

 the amount of iron salts present. 



With the sulphuric-acid solution already given the electro- 

 motive force varied from 0*0033 to 0'0078 of a volt, while 

 with the nitric-acid solution it became as great as 0*036 of a 

 volt. In making all the solutions used with the different 

 substances amounts were taken proportional to their particular 

 molecular weights, and then halved or doubled until of suit- 

 able strength to give results with the galvanometer. It was 

 thought possible at the beginning that this might lead to 

 some relations between the protective results and the strengths 

 of the particular solutions ; but the general irregular cha- 

 racter of the whole phenomenon prevented comparisons in 

 this respect, and all that can be stated is, that both the 

 " protective throw " and the concentration effect in general 

 increased rapidly with the strength of the solution. 



H. Influence of a Periodic Magnetic Field upon the Cell. 



An experiment was made to determine the behaviour of the 

 standard nitric-acid cell when the magnetic field was made 

 and broken at regular intervals over a considerable time, and 

 curves were drawn showing the variation of the " throw " with 



