1884.] 



On Magnetic Polarity and Neutrality. 



409 



the reactions in the solid bar being more pronounced and complete 

 than those obtained through a separation of air ; the greater the separa- 

 tion the less the reaction, but in no case will the law of neutrality be 

 changed. 



In homogeneous iron or steel, we have a well-defined curve, the 

 distance of which can be calculated from observation upon thf* 

 remaining magnetism, but if the interior is harder than the exterior, 

 the inner portion will from its rigidity preserve its previous magne- 

 tism, reversing entirely the outer portions. This occurs also in small 

 electro-magnets where from the small number of molecules in the 

 interior compared with the vastly greater exterior, and also all the 

 surrounding inducing lines of magnetic force acting on the centre 

 from all sides, the outside is completely reversed to a remarkable 

 depth. 



I have been enabled to prove this by the chemical method, em- 

 ploying either dilute sulphuric acid, acidulated bichromate of potass, 

 or dilute nitric acid (1 pint acid to 5 water), the latter being far more 

 rapid and equal in its action. The following experiment will show 

 rapidly the influence of the outside reversal polarity. Let us take a 

 soft steel wire 1 millim. diameter, 10 centims. long. Magnetise it in a 

 coil, or by drawing over a strong permanent magnet, so that it has 

 perhaps a remaining magnetism of 200°. If we vibrate this rod or give 

 several blows from a mallet, we can reduce this to 25° ; we have now 

 almost perfect neutrality, having only a remaining magnetism of 25°, 

 which remains a constant for years if not remagnetised. Place 

 this rod in dilute nitric acid, and in fifteen minutes it will rise 

 to 50°, or double its previous value, in one hour to 75°, and two or 

 three hours to 100°, or four times its previous force ; the increased 

 force of 75° has been rendered evident by dissolving an equal 

 opposing polarity of 75°, so that we have already found 75 + 75 + 25 

 = 175°, or 87 per cent, of its highest force. This is so easily repeated 

 with soft steels of all sizes and dimensions, that there can no longer 

 be any doubt as to the existence of the outside reversed polarity. 

 The experiment is more difficult to repeat with soft iron, as from the 

 freedom of its molecules a fresh outside reversed curve is formed 

 anew as the exterior is dissolved, the balancing curves reproducing 

 themselves until we have almost entirely dissolved the iron ; still with 

 care, and iron not too soft, we can render evident all the neutral 

 curves seen in steel.* 



The curves obtained by the various methods are so numerous, each 

 requiring more space than the limits of this paper will allow, that I 



* Thin flat steel, such as clock-springs, saw-blades, or ribbon steel, well annealed, 

 are most suitable for this experiment. They may be of any width or length ; the 

 thickness may vary between 5 and f millim. I have found that strips of | millim, 

 thick give the highest result. 



