246 HEXKY A. EOWLAND 



Several things are worthy of note in this 'list. In the first place 

 those solutions of metallic salts which are precipitated by iron all show 

 distinct signs of protective action when the current is passed through 

 the magnet. Of the various acids this is not generally true ; only those 

 show the magnetic effect, which act on iron without the evolution of 

 hydrogen, and are powerful oxidizing agents. In general, substances 

 which acted without the evolution of hydrogen gave an effect with the 

 magnet. 



From these experiments it was quite evident that the protective 

 action, whatever its cause, was more general than at first appeared and 

 steps were next taken to extend it to the other magnetic metals. Small 

 bars were made of nickel and cobalt and tried in the same manner as 

 before. These metals are acted on but very slightly by most acids, and 

 the range of substances which could be used was therefore very small, 

 but all the substances which gave the magnetic effects with iron poles 

 gave a precisely similar, though much smaller effect, whenever they 

 were capable of acting at all on the nickel and cobalt. This was notably 

 the case with nitric acid, bromine water, chlorine water, and platinum 

 tetrachloride, which were the substances acting readily on the metals in 

 question. Even with these powerful agents, however, the magnetic 

 action was very much less than with iron, and experimentation on 

 metals even more weakly magnetic was evidently hopeless. 



As a preliminary step toward ascertaining the cause* of the magnetic 

 action and its non-appearance where the active substance evolved hydro- 

 gen, it now became necessary to discover and if possible eliminate the 

 cause of the reversal of the current which regularly followed the protec- 

 tive throw. Experiments soon showed that it could not be ascribed to 

 accumulation of decomposition products around the electrodes, and 

 polarization, while it could readily neutralize the original deflection, 

 could not reverse its direction. Whatever the cause, it was one which 

 did not act with any great regularity, and it was soon found that stirring 

 the liquid while the magnet was on, uniformly produced the effect ob- 

 served. Since one pole was simply exposed over a small portion of its 

 side while the other had a sharp projecting point, it was the latter which 

 was most freely attacked when there were currents in the liquid, whether 

 these were stirred up artificially or were produced by the change in gal- 

 vanic action due to the presence of the magnet. AVhen the poles were 

 placed in fine sand saturated with acid this reversing action was much 

 diminished, and in fact anything which tended to hinder free circulation 

 of the liquid produced the same effect. Several materials were tried and 



