﻿430 
  Dr. 
  J. 
  Erskine-Murray 
  on 
  

  

  The 
  copper 
  plate 
  was 
  now 
  gently 
  heated 
  with 
  a 
  bolt 
  until 
  it 
  

   was 
  hot 
  enough 
  to 
  melt 
  paraffin-wax 
  ; 
  the 
  temperature, 
  about 
  

   50° 
  C, 
  required 
  for 
  this 
  is 
  not 
  sufficient 
  to 
  cause 
  sudden 
  

   permanent 
  change 
  of 
  the 
  copper 
  surface 
  (see 
  § 
  74). 
  Paraffin- 
  

   wax 
  was 
  then 
  poured 
  on, 
  and 
  the 
  plate 
  was 
  filed 
  with 
  its 
  own 
  

   file 
  while 
  covered 
  with 
  molten 
  wax. 
  Thus 
  the 
  fresh 
  surface 
  

   exposed 
  by 
  the 
  filing 
  came 
  directly 
  into 
  contact 
  with 
  the 
  

   wax. 
  More 
  wax 
  was 
  poured 
  on 
  and 
  the 
  filings 
  drained 
  oft', 
  

   the 
  plate 
  remaining 
  well 
  covered 
  with 
  wax 
  all 
  the 
  while. 
  It 
  

   was 
  then 
  allowed 
  to 
  cool, 
  and 
  gave 
  with 
  the 
  bare 
  zinc 
  plate 
  

  

  + 
  •555 
  v., 
  

  

  zinc 
  being 
  positive 
  as 
  before. 
  Thus 
  the 
  change 
  due 
  to 
  

   substituting 
  paraffin-wax 
  for 
  air 
  next 
  the 
  copper 
  is 
  not 
  more 
  

   than 
  + 
  "100 
  v. 
  I 
  now 
  waxed 
  the 
  zinc 
  in 
  exactly 
  the 
  same 
  

   way. 
  When 
  it 
  was 
  quite 
  cool 
  it 
  gave 
  with 
  the 
  waxed 
  copper 
  

  

  + 
  •602 
  v., 
  

  

  showing 
  that 
  waxing 
  the 
  zinc 
  had 
  raised 
  its 
  potential 
  

  

  + 
  •047 
  v. 
  

  

  So 
  on 
  the 
  whole, 
  the 
  substitution 
  of 
  wax 
  for 
  air 
  on 
  both 
  

   copper 
  and 
  zinc 
  had 
  only 
  decreased 
  their 
  mutual 
  potential 
  by 
  

  

  + 
  053 
  v. 
  

  

  and 
  the 
  potential 
  of 
  the 
  waxed 
  plates 
  remained 
  nearly 
  

   constant 
  for 
  several 
  hours. 
  The 
  changes 
  due 
  to 
  waxing 
  the 
  

   plates 
  as 
  given 
  above 
  were 
  confirmed 
  by 
  the 
  independent 
  

   comparison 
  of 
  each 
  plate 
  with 
  the 
  standard 
  gold 
  plate. 
  It 
  

   does 
  not 
  follow 
  that 
  even 
  the 
  small 
  changes 
  which 
  did 
  occur 
  

   were 
  due 
  solely 
  to 
  the 
  substitution 
  of 
  wax 
  for 
  air, 
  for 
  they 
  

   may 
  have 
  been 
  caused 
  by 
  slight 
  changes 
  in 
  the 
  surface 
  on 
  

   account 
  of 
  the 
  filing. 
  

  

  § 
  80. 
  An 
  aluminium 
  plate 
  was 
  coated 
  with 
  wax 
  in 
  the 
  way 
  

   described 
  in 
  § 
  79, 
  a 
  knife 
  being 
  used 
  to 
  scrape 
  the 
  surface 
  

   under 
  the 
  molten 
  wax. 
  When 
  cold, 
  this 
  waxed 
  plate 
  gave 
  

   with 
  a 
  bare 
  zinc 
  one 
  

  

  + 
  •36 
  v., 
  

  

  which 
  is 
  about 
  the 
  usual 
  value 
  for 
  bare 
  aluminium 
  and 
  zinc. 
  

   The 
  removal 
  of 
  the 
  air 
  had 
  therefore 
  not 
  appreciably 
  altered 
  

   the 
  potential. 
  

  

  § 
  81. 
  I 
  now 
  warmed 
  the 
  waxed 
  aluminium 
  slightly. 
  Its 
  

   potential 
  with 
  the 
  zinc 
  varied 
  as 
  follows 
  : 
  — 
  

  

  47° 
  C 
  + 
  -41 
  v. 
  

  

  35° 
  C 
  +-37 
  v. 
  

  

  28° 
  C 
  +-35 
  v. 
  

  

  