42 H. A. Rowland and L. Bell — Explanation of the 



ing like a miniature storage battery which promptly discharged 

 itself when the charging was discontinued by breaking the cur- 

 rent through the magnet. The gradual reversal of the current 

 some little time after exciting the magnet was noted frequently 

 in these cases, as before. Owing to this peculiarity and their 

 generally very irregular action, the various salts were disagree- 

 able substances to experiment with, though as a rule they gave 

 positive results. 



Unless the poles were kept cleau experimenting became 

 difficult from the accumulation of decomposition products 

 about them and oxidation of their surfaces. A few experi- 

 ments showed how easily the original deflection could be mod- 

 ified, nearly annulled or even reversed in direction by slight 

 differences in the condition of the poles. These difficulties of 

 the method are, however, more than counterbalanced by its 

 rapidity and delicacy when proper precautions are taken. 



Xearly thirty substances were tested in the manner previ- 

 ously described ; but comparatively few of them gave very 

 decided effects with the magnet, though, as later experiments 

 have shown, the protective action is a general one. The sub- 

 stances first tried were as follows. The table shows the various 

 acids and salts tried, and their effects as shown by the original 

 apparatus : 



Substances. 



Effect due to 

 magnet. 



Xotes. 



Nitric acid 



Strong. 



Always powerful protective throw. 



Sulphuric " 



Little or none. 



Does not act very readily on the iron. 



Hydrochloric acid 



" ;t 





Acetic " 



Xone. 





Formic li 







Oxalic " 



" 





Tartaric " 



a 





Chromic " 



Some effect. 



Sometimes quite distinct throw, irregular. 



Perchloric " 





Much less marked than with chromic. 



Chloric " 



Xone. 





Bromic " 



" 





Phosphoric " 



K 



Hardly any effect on iron. 



Permanganic i; 



Slight effect. 



More than with perchloric. 



Chlorine water 



Decided li 





Bromine " 



" 





Iodine " 



u 





Copper sulphate 



a 



Mainly showing as throw, on breaking. 



" nitrate _._ 



Some. 



U W (( 



" acetate 





(. I( 



" chloride 





(I 11 It 



" tartrate 



Slight. 





Mercuric bromide 



Some. 



Throw, on breaking. 



" chloride 



.1 



Yery slight solution, weak. 



Mercurous nitrate 



" 



Mainly as throw on breaking. [breaking. 



Ferric chloride 



Decided. 



'Both protective throw, and sometimes on 



Silver nitrate 



Some. 



Action very irregular. 



Platinum tetrachloride. 



it 



" " 



