122 Mr. T. Andrews. [June 5, 



magnetised bar ; this more extended fling of the galvanometer, how- 

 ever, subsided in a few seconds, and did not interfere with after 

 results due to electro-chemical action. 



The results of Series I, in cold nitric acid, were perhaps more per- 

 eeptible in those experiments extending over the longer periods (see 

 Table I), though even in these, the effect was comparatively small. In 

 a recent research by the author on " Electro-chemical Effects on 

 Magnetising Iron," Part II (' Roy. Soc. Proc.,' vol. 44, p. 152), it 

 was noticed that local currents were set up between the polar 

 terminals and central portions of steel magnets exposed in electro- 

 lytes, and this class of local action, together with the slight alteration 

 of the physical structure of the magnet bars consequent on their 

 magnetisation, may possibly be involved in producing the effects due 

 to magnetism on passive steel or iron in concentrated nitric acid. 

 The influence of magnetism of low intensity, whilst modifying to a 

 very limited extent, does not, however, appear sufficient entirely to 

 overcome, the passivity of the metal in nitric acid, and the influence 

 of even a powerful magnetic force, though doubtle&s slightly modify- 

 ing (to the extent, possibly, of the slight alteration of physical state 

 in the metals, induced by magnetism), did not destroy the passivity 

 of bright iron or steel exposed to its action in cold strong nitric 

 acid. 



The whole of the results on Table I afford an indication that mag- 

 netisation of comparatively low intensity, acting during considerable 

 periods of time, exerts only a limited modifying influence on the 

 passivity of iron or steel in the cold, or up to a temperature of about 

 60 F., though the influence is just discernible when employing a 

 delicate galvanometer. Magnetisation, with the nitric acid at a 

 higher temperature, produces a quicker effect, see results in Series II, 

 Table II. The author is pleased to see that somewhat similar con- 

 clusions as to the influence of powerful magnetisation on the passive 

 state of powdered iron in warm nitric acid have been independently 

 arrived at in America by Messrs. Nichols and Franklin, who, in some 

 recent interesting experiments, have found that powdered iron in 

 nitric acid, 1'368 sp. gr., when placed in a test-tube in a suitable 

 apparatus between the poles of a powerful electro-magnet commenced 

 to be violently acted upon when raised to a temperature of 51 C. 

 Unmagnetised iron usually remains passive in strong nitric acid 

 until a temperature of about 89 C. is reached, when an explosion, 

 consequent on loss of passivity, occurs. Messrs. Nichols and 

 Franklin's experiments, therefore, show that very powerful magnetic 

 action helps to lower the temperature of transition from the passive 

 to the active state. They have also found that " the intensity of the 

 magnetic field necessary to convert passive into active iron at a given 

 temperature increases rapidly with the concentration of the acid." 



