452 G. 0. Squier — Electro- Chemical 



tion. By making the conditions still more unfavorable for the 

 •'protective throw," it gradually diminished until entirely 

 masked by the second effect, so that making the field produced 

 a deflection in the direction indicating a current from the 

 point. 



"With the proper conditions both of these effects could be 

 studied with the greatest ease : first, one made prominent, then 

 both equal, then the other made prominent at will. The "pro- 

 tective throw " could be traced until it became a mere sta- 

 tionary tremor of the needle at the instant of its starting on 

 the " concentration throw." This latter, though called a 

 "throw," can be made to vary from an extremely slow continu- 

 ous movement of the galvanometer deflection, as in experiment 

 £, already described, to a comparatively rapid deflection at the 

 instant of making the magnet. 



By using simply a dilute nitric acid solution with no gelatine, 

 and inserting a thick piece of glass between the electrodes, the 

 concentration effect was delayed enough to allow the " protec- 

 tive throw" to first appear, with considerable iron salts in the 

 solution, and on making the field both effects were observed 

 as described above. 



It now appears that the reversal of the current uniformly 

 observed in the experiments of Messrs. Rowland and Bell was 

 but a form of the " concentration throw " mentioned above, 

 and that we can regard the substitution of the hardened acidu- 

 lated gelatine for the dilute acid, as merely separating these 

 effects, so that the former can be studied by itself ; in other 

 words, the reversal of the current would have occurred just 

 the same after a sufficient time had elapsed. 



Turning to the experiments of Drs. Gross and Andrews, 

 they employed but one magnetized electrode which was not 

 pointed. In this case the nature of the magnetic field at the 

 two exposed surfaces would be very much more nearly the 

 same than when a pointed electrode is employed. This arrange- 

 ment is not therefore suited to bring out the delicate "protec- 

 tive throw," and it is not surprising that the concentration 

 effect was the prominent feature observed. 



We have now a complete reconciliation of the directly op- 

 posite results referred to in the introduction. The " protec- 

 tive throw " is due to the actual attraction of the magnet for 

 the iron, and is always in the direction to protect the more 

 strongly magnetized parts, while the " concentration throw " 

 is always in the opposite direction, and depends upon the dis- 

 tribution of the iron salts present in the solution, and the con- 

 vection currents in the liquid. The concentration of the 

 products of the reaction about the point, would tend to pro- 

 duce a ferrous reaction instead of a ferric reaction, and experi- 



