Abstracts of Technical Articles from Bell System Sources 



Barkhansen Effect II. Determination of the Average Size of the 

 Discontinuities in Magnetization} R. M. Bozorth and J. F. Dil- 

 LINGER. When the magnetic field-strength acting on a ferro-magnetic 

 material is changed, the magnetization changes discontinuously (Bark- 

 hausen effect). These discontinuous changes have been examined in 

 1 mm. wires; an expression is derived and experimental arrangements 

 are described for determining their average size for a given material 

 in a given state of magnetization. 



Experimental determinations of the average size have been made 

 for iron (including a single crystal and a hard-drawn wire), nickel, and 

 several iron-nickel alloys (permalloys). The average size is greatest 

 on or near the steepest part of the hysteresis loop. The greatest aver- 

 age size, expressed as the volume of material the magnetization of which 

 must be changed from saturation in one sense to saturation in the 

 opposite sense to produce the same change in magnetization, is much 

 the same for all of the materials examined, the extremes being 1.2 x 10~^ 

 cm.'' for annealed iron and 45 x io~^ cm.^ for 50 per cent nickel per- 

 malloy. This shows that the sizes of the discontinuities do not depend 

 to any considerable extent on the size or kind of crystals. 



Criticism is made of previous work on the size of the coherence re- 

 gion, the region within which the change in magnetization is confined. 

 Although the effect of a single discontinuity in magnetization may be 

 detected as far as 10 cm. from its source because of the eddy-currents 

 induced, the experimental evidence is consistent with the view that 

 the permanent change in magnetization is confined to the volume in 

 terms of which the size of the discontinuity is measured as stated above, 

 always less than 10~^ cm.^. 



Particle Size as a Factor in the Corrosioji of Lead by Soils.- R. M. 

 Burns and D. J. Salle v. In order to determine that part which 

 particle size plays in the corrosion of lead by soils, lead specimens were 

 buried in sands (generally inert in character) of various particle sizes 

 and were maintained for periods of time ranging from 8 days to 5 

 months at 40° C. in a closed system in which the humidity and the 

 composition of the atmosphere were controlled. 



' Phys. Rev., Apr. 1, 19.30. 



- Ind. and Engg. Cliem., Mar., 1930. 



595 



