﻿160 
  Mr. 
  D. 
  E. 
  Roberts 
  on 
  the 
  Effect 
  of 
  Temperature 
  and 
  

  

  occur 
  in 
  minute 
  quantities 
  as 
  impurities 
  ; 
  many 
  varieties 
  

   contain 
  as 
  much 
  as 
  99 
  per 
  cent, 
  of 
  pure 
  carbon. 
  The 
  

   chemical 
  structure 
  of 
  graphite 
  is 
  probably 
  a 
  complicated 
  one, 
  

   but 
  above 
  370° 
  C. 
  graphite 
  is 
  the 
  most 
  stable 
  of 
  the 
  three 
  

   allotropic 
  modifications 
  of 
  carbon. 
  Its 
  optical 
  constants 
  were 
  

   lately 
  determined 
  by 
  Zakrewski*. 
  

  

  Several 
  properties 
  of 
  graphite 
  have 
  been 
  investigated 
  by 
  

   Koenigsberger 
  f 
  and 
  his 
  co-workers 
  ; 
  its 
  conductivity 
  for 
  

   heat 
  along 
  its 
  base-plane 
  and 
  also 
  at 
  right 
  angles 
  to 
  its 
  axis 
  

   was 
  found 
  to 
  have 
  a 
  very 
  high 
  value, 
  viz., 
  0*85 
  (cal./cm. 
  

   sec. 
  °C), 
  which 
  nearly 
  equals 
  that 
  of 
  copper 
  (0*9) 
  ; 
  this 
  does 
  

   not, 
  however, 
  at 
  all 
  agree 
  with 
  the 
  law 
  of 
  Wiedemann 
  and 
  

   Franz. 
  

  

  They 
  further 
  (/. 
  c.) 
  investigated 
  its 
  thermoelectric 
  effect 
  

   (compared 
  with 
  copper) 
  and 
  its 
  Thomson 
  effect, 
  but 
  found 
  

   here 
  no 
  extreme 
  values. 
  

  

  According 
  to 
  a 
  private 
  communication 
  kindly 
  sent 
  to 
  me 
  

   by 
  Prof. 
  Koenigsberger, 
  Gottstein 
  J 
  found 
  for 
  the 
  Hall 
  

   effect 
  in 
  the 
  variety 
  of 
  graphite 
  which 
  I 
  term 
  below 
  G 
  V., 
  

   R=— 
  0*71. 
  In 
  the 
  case 
  of 
  variety 
  I., 
  which 
  I 
  preferably 
  

   worked 
  with, 
  the 
  Hall 
  effect 
  was 
  found 
  in 
  an 
  experiment 
  by 
  

   Washburne 
  to 
  be 
  of 
  the 
  same 
  order, 
  but 
  showed 
  marked 
  

   dissymmetry. 
  

  

  The 
  following 
  values 
  of 
  the 
  specific 
  resistance 
  of 
  graphite 
  

   were 
  found 
  by 
  Mnraoka, 
  Artom, 
  Piesch, 
  Koenigsberger 
  and 
  

   Weiss 
  §: 
  — 
  

  

  Ceylon 
  graphite 
  at 
  0° 
  12 
  . 
  10 
  ~ 
  4 
  ohm 
  per 
  c.c. 
  

  

  Siberian 
  graphite 
  at 
  0° 
  11 
  . 
  10 
  " 
  4 
  „ 
  „ 
  

  

  Greenland 
  graphite 
  at 
  15° 
  ... 
  4.10 
  -4 
  „ 
  „ 
  

  

  Ceylon 
  graphite 
  at 
  16°.... 
  3*6 
  . 
  10~ 
  4 
  „ 
  

  

  On 
  the 
  other 
  hand, 
  my 
  best 
  graphite 
  pieces 
  of 
  the 
  variety 
  GI 
  . 
  

   gave 
  a 
  specific 
  resistance 
  as 
  low 
  as 
  0*5 
  . 
  10 
  -4 
  , 
  i. 
  e. 
  almost 
  half 
  

   that 
  of 
  mercury 
  (0*96 
  . 
  10~ 
  4 
  at 
  18°). 
  This 
  material 
  also, 
  at 
  

   ordinary 
  temperatures, 
  showed 
  an 
  increase 
  of 
  resistance 
  of 
  

   + 
  0*001 
  per 
  degree 
  rise 
  of 
  temperature, 
  while 
  at 
  high 
  and 
  

   low 
  temperatures 
  the 
  increase 
  was 
  +0*0025 
  per 
  degree 
  

  

  * 
  K. 
  Zakrewski, 
  Bull. 
  Int. 
  Acad. 
  Cracow, 
  (A) 
  xxii. 
  p. 
  122 
  (1910). 
  

  

  t 
  J. 
  Koenigsberger 
  and 
  J. 
  Weiss, 
  Ann. 
  d. 
  Phys. 
  xxxv. 
  p. 
  27 
  (1911) 
  ; 
  

   Verh. 
  d. 
  Phys. 
  Ges. 
  xiv. 
  p. 
  9 
  (1912) 
  ; 
  J. 
  Weiss, 
  Inaug.-Diss., 
  Freiburg 
  

   i. 
  B. 
  (1910). 
  

  

  % 
  This 
  will 
  soon 
  be 
  published 
  in 
  a 
  Dissertation. 
  

  

  § 
  Cf. 
  Handh. 
  d. 
  Anorg. 
  Chem. 
  iii. 
  (2 
  Abt.) 
  p. 
  54 
  (1909); 
  J 
  .Koenigs- 
  

   berger 
  and 
  J. 
  Weiss, 
  Ann. 
  d. 
  Pys. 
  xxxv. 
  p. 
  2 
  (1911). 
  

  

  