﻿Magnetization 
  on 
  the 
  Resistance 
  of 
  Graphite. 
  159 
  

  

  exhibit 
  an 
  increase 
  of 
  resistance 
  when 
  magnetized, 
  while 
  the 
  

   three 
  ferromagnetic 
  metals, 
  at 
  least 
  in 
  sufficiently 
  strong 
  

   transverse 
  fields, 
  show 
  a 
  decrease. 
  Although, 
  as 
  yet, 
  no 
  

   simple 
  relation 
  has 
  been 
  found 
  to 
  exist 
  between 
  the 
  order 
  of 
  

   magnitude 
  of 
  this 
  effect 
  and 
  the 
  corresponding 
  magnetic 
  

   susceptibility, 
  it 
  may 
  be 
  noticed 
  that 
  the 
  effect 
  is 
  a 
  hundred 
  

   times 
  greater 
  for 
  diamagnetic 
  cadmium 
  than 
  for 
  para- 
  

   magnetic 
  tantalium 
  and 
  again 
  a 
  thousand 
  times 
  greater 
  for 
  

   bis 
  in 
  nth. 
  This 
  element, 
  as 
  is 
  well 
  known, 
  possesses 
  rather 
  a 
  

   high 
  diamagnetic 
  specific 
  susceptibility 
  ( 
  — 
  1*40 
  . 
  10~ 
  6 
  ). 
  Soon 
  

   after 
  Morris 
  Owen* 
  found 
  Ceylon 
  graphite 
  to 
  show 
  the 
  

   highest 
  susceptibility 
  yet 
  observed, 
  Dr. 
  W. 
  J. 
  do 
  Haas 
  was 
  

   led 
  by 
  analogy 
  to 
  anticipate 
  that 
  graphite 
  might 
  exhibit 
  a 
  

   variation 
  of 
  resistance 
  of 
  an 
  even 
  higher 
  order 
  when 
  

   magnetized, 
  and 
  suggested 
  to 
  me 
  to 
  search 
  for 
  the 
  effect. 
  

   The 
  preliminary 
  experiments 
  | 
  performed 
  with 
  powdered 
  

   graphite 
  pressed 
  into 
  a 
  thin 
  plate, 
  with 
  irregularly 
  shaped 
  

   pieces, 
  and 
  with 
  ordinary 
  pencils, 
  amply 
  satisfied 
  expectation, 
  

   and 
  justified 
  an 
  extended 
  investigation 
  of 
  the 
  phenomenon. 
  

   Graphite 
  crystallizes 
  in 
  the 
  hexagonal 
  rhombohedral 
  (or 
  

   according 
  to 
  the 
  new 
  notation, 
  the 
  ditrigonal 
  scalenohedral) 
  

   form 
  ; 
  it 
  was 
  once 
  assigned 
  to 
  the 
  monoclinic 
  class 
  of 
  

   crystals, 
  but 
  latterly 
  this 
  view 
  appears 
  to 
  have 
  little 
  support. 
  

   Fairly 
  well-defined 
  crystalline 
  pieces 
  are, 
  with 
  few 
  exceptions, 
  

   only 
  found 
  in 
  Pargas 
  (Finland) 
  and 
  Ticonderoga 
  (New 
  York) 
  ; 
  

   of 
  the 
  former 
  I 
  succeeded 
  in 
  obtaining 
  a 
  few 
  specimens. 
  

   Most 
  frequently 
  graphite 
  is 
  found 
  filling 
  veins, 
  or 
  in 
  compact 
  

   laminated 
  masses, 
  or 
  as 
  isolated 
  flakes 
  or 
  scales 
  embedded 
  in 
  

   the 
  older 
  crystalline 
  rocks 
  ; 
  it 
  possesses 
  perfect 
  basal 
  cleavage, 
  

   and 
  can 
  thus 
  be 
  obtained 
  in 
  thin 
  plates 
  or 
  flakes 
  which 
  are 
  

   soft 
  and 
  flexible 
  but 
  not 
  elastic. 
  

  

  Its 
  density 
  appears 
  to 
  be 
  very 
  variable. 
  Le 
  Chatelier 
  and 
  

   AVologdin 
  % 
  have 
  systematically 
  investigated 
  artificial 
  

   graphite 
  made 
  after 
  Acheson 
  and 
  that 
  obtained 
  from 
  cast- 
  

   iron, 
  as 
  well 
  as 
  native 
  graphite 
  from 
  Scharzbach 
  and 
  Mograu 
  

   (Bohemia), 
  Siberia, 
  Ceylon, 
  and 
  Australia. 
  The 
  density 
  

   varied 
  between 
  1*6 
  and 
  2*2 
  ; 
  after 
  the 
  graphite 
  had 
  been 
  

   purified 
  by 
  solutions 
  of 
  potash, 
  &c, 
  and 
  subjected 
  to 
  pressure, 
  

   all 
  the 
  samples 
  agreed 
  in 
  giving 
  a 
  density 
  of 
  2255 
  (H 
  2 
  at 
  

   4° 
  C). 
  Lime, 
  silicic 
  acid, 
  iron, 
  and 
  carburetted 
  hydrogen 
  

  

  * 
  Morris 
  Owen, 
  Versl. 
  Afd. 
  Natuurkd. 
  xx. 
  p. 
  673 
  (1911); 
  Ann. 
  dcr 
  

   Phi/sik, 
  xxxvii. 
  p. 
  657 
  (1912). 
  

  

  t 
  When 
  transversely 
  magnetized 
  in 
  a 
  field 
  of 
  20 
  kgs. 
  the 
  compressed 
  

   Ceylon 
  graphite 
  gave 
  an 
  increase 
  of 
  resistance 
  of 
  52 
  per 
  cent.; 
  an 
  

   irregularly-shaped 
  piece 
  gave 
  an 
  increase 
  of 
  219 
  per 
  cent. 
  ; 
  II 
  B 
  and 
  SB 
  

   pencils 
  by 
  A. 
  W. 
  Faber 
  gave 
  only 
  a 
  3 
  per 
  cent, 
  increase. 
  The 
  best 
  

   sample 
  GL 
  15 
  gave 
  as 
  much 
  as 
  400 
  per 
  cent. 
  

  

  X 
  H. 
  le 
  Chatelier 
  and 
  S. 
  Wologdin, 
  Compt. 
  Rend, 
  cxlvi. 
  p. 
  49 
  (1908). 
  

  

  