MAGNETIC METHODS 



179 



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by adjusting the potentiometer. The magnetic moment may be calculated 

 from the change in potentiometer setting or ratio of current in the two 

 coils and the constants of the apparatus. Knowing the magnetic moment 

 of the specimen, the intensity of magnetization / may be calculated from the 

 relation : / = magnetic moment per unit volume. 



Another instrument for testing cores ....... ..^^^^^ ^ 



comprises a core suspended on a fibre and iiiii^ 



placed in a magnetic field. The core as- 

 sumes an orientation indicating its direc- 

 tion of magnetization. f 



An Improved Type of Two Sole- 

 noid Instrument. — An astatic suscepti- 

 bility meter was developed and tested by 

 R. C. LoringI in 1939, by means of which 

 the complete hysteresis curve for a shaped 

 rock sample could be determined. It is 

 similar in design to the apparatus used by 

 Ambronn, as shown in Figure 74, with 

 one exception. In the Loring instrument 

 one of the solenoids carries a secondary 

 winding through which a measured cur- 

 rent can be passed. 



In operating this instrument it is neces- 

 sary first to carefully adjust the position 

 of the two solenoids, which are identical 

 in size and shape. They are set so that with 

 a certain current flowing through their 

 primary winding no deflection is produced 

 on the magnetic system of the instrument. 

 With the current still flowing a test sample 

 is then put in the solenoid (having the 

 secondary winding) which will cause a 

 deflection. This deflection is neutralized by 

 setting a current in the auxiliary, or sec- 

 ondary, winding at such a value that, 

 again, no deflection is obtained. The 

 amount of such current, in milliamperes, 



required to neutralize the deflection is a measure of the induction in the 

 test specimen resulting from the original current or field in the solenoids. 



The above apparatus is quite versatile. For example, if a deflection is 

 evident when a sample is placed in the solenoid that carries the two windings 

 when no current is flowing, it would indicate that the sample had certain 



t Randall Wright, U. S. Pat. 2,147,942, issued Feb. 21, 1939. 



t Loring, R. C. ; The Design and Calibration of an Astatic Susceptibility Meter; (unpublished) 

 thesis for M.S. degree, Library, Colorado School of Mines, Golden, Colorado, May, 1939. 



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Fig. 74. — Method for determining mag- 

 netic susceptibility. C and C, two iden- 

 tical solenoids with like poles opposing; 

 M, mirror; n and s, astatic magnetic 

 system; T, torque head; F, suspension 

 fibre; H and H', specimen holders, 

 usually glass, in one of which is placed 

 solid or pulverized specimen; L, leveling 

 points; P, potentiometer; MA, milliam- 

 pere meter; B, battery. 



