424 Nichols and Franklin — Destruction of the 



mated by withdrawing a coil of small area from the field and 

 comparing the consequent swing of a galvanometer needle with 

 that produced in the same needle by a Weber's " earth- inductor." 



"With this apparatus the influence of magnetization upon the 

 passivity of iron was studied under various circumstances. It 

 was found very difficult, even with the knowledge of other 

 causes of variation in the temperature of transition, gained by 

 the preliminary experiments, to obtain entirely concordant 

 results ; but a number of interesting facts concerning the influ- 

 ence of the magnet were established. The following is a resume' 

 of notes made during the investigation : 



(a). 8 C0 of HNO 3 , sp. gr. 1*368, acting upon 1 gram of iron 

 in the magnetic field. The tube containing the iron and acid 

 was immersed in water, which up to the beginning of the ex- 

 periment, had been boiling. The strength of the field, which 

 was insufficient to destroy passivity at the temperature of the 

 room (20°), was not measured. 



Effervesence ' began at once and increased, until the ther- 

 mometer indicated 51°, when the explosion, characteristic of 

 loss of passivity occurred, blowing most of the liquid from the 

 tube. The remainder became quiescent again, but when 

 touched with the thermometer-bulb its explosive activity re- 

 turned. The reaction differed apparently in its nature from 

 that taking place out of the field. The products of the reac- 

 tion when poured from the tube, left the tube and thermome- 

 ter-bulb clean, whereas, after the ordinary reaction they were 

 thickly coated with a black residue, the removal of which 

 necessitated long boiling in acid. 



(b). .A repetition of experiment (a), with the magnet not 

 acting. The thermometer rose steadily to 89°, at which tem- 

 perature the transition to the active state took place. 



(c). Conditions those of experiment (a), magnet acting. Tem- 

 perature of transition was 51°. It was noticed that passivity 

 was not lost throughout the mass of powdered iron at once, but 

 began at a single point on the side of the tube, whence streams 

 of gas were evolved while the rest of the iron remained pas- 

 sive. From this, as a center, the action spread, until the entire 

 mass became involved. The temperature noted was that at 

 which activity had become general. 



(d). Conditions those of the experiment (a), excepting that 

 the magnet was inactive until the temperature of the solution 

 reached 60°, when the circuit was closed. Passivity was de- 

 stroyed at once by the action of the magnet. 



(e). Conditions those of experiment (a), excepting that the 

 circuit was made and broken at every degree from 40° up- 

 ward. But little effect was produced until in the neighbor- 

 hood of 60°, when each tap of the key was marked by mo- 



