﻿218 
  Scientific 
  Intelligence. 
  

  

  the 
  thermopile, 
  and 
  is 
  capable 
  of 
  exact 
  setting 
  in 
  the 
  spectrum. 
  

   To 
  offset 
  these 
  advantages, 
  the 
  thermopile 
  requires 
  no 
  battery 
  or 
  

   balancing 
  coils, 
  and 
  costs 
  but 
  about 
  one-thirtieth 
  as 
  much 
  as 
  the 
  

   bolometer 
  with 
  its 
  necessary 
  accessories. 
  Nevertheless, 
  to 
  make 
  

   it 
  equal 
  to 
  the 
  bolometer 
  as 
  regards 
  " 
  wiggle 
  " 
  and 
  " 
  drift 
  " 
  and 
  

   capacity 
  for 
  accurate 
  setting, 
  it 
  would 
  require 
  a 
  mounting 
  at 
  least 
  

   a 
  fourth 
  as 
  costly 
  as 
  the 
  bolometer 
  and 
  its 
  accessories. 
  On 
  the 
  

   whole 
  the 
  bolometer 
  has 
  the 
  advantage, 
  except 
  in 
  cost. 
  

  

  2. 
  The 
  Electro- 
  Chemical 
  Equivalents 
  of 
  Copper 
  and 
  Silver 
  ;* 
  

   by 
  Theodore 
  W. 
  Richards, 
  E. 
  Collins 
  and 
  G. 
  W. 
  Heimrod. 
  — 
  

   Since 
  Faraday 
  pointed 
  out 
  in 
  1833 
  that 
  the 
  amounts 
  of 
  

   different 
  substances, 
  separated 
  in 
  successive 
  cells 
  by 
  a 
  given 
  

   current 
  of 
  electricity, 
  are 
  proportional 
  to 
  the 
  chemical 
  equiva- 
  

   lents 
  of 
  the 
  several 
  substances, 
  numerous 
  attempts 
  have 
  been 
  

   made 
  to 
  verify 
  this 
  important 
  law 
  with 
  rigid 
  accuracy. 
  None 
  of 
  

   these 
  attempts 
  have 
  been 
  very 
  successful, 
  since 
  there 
  are 
  so 
  many 
  

   possibilities 
  of 
  error, 
  owing 
  to 
  " 
  side 
  reactions," 
  in 
  the 
  determi- 
  

   nation 
  both 
  of 
  the 
  electrochemical 
  and 
  the 
  strictly 
  chemical 
  

   equivalents. 
  The 
  two 
  metals 
  most 
  convenient 
  for 
  the 
  practical 
  

   application 
  of 
  this 
  principle 
  are 
  copper 
  and 
  silver, 
  and 
  it 
  seemed 
  

   likely 
  that 
  a 
  careful 
  comparative 
  study 
  of 
  the 
  copper 
  and 
  silver 
  

   il 
  voltameters 
  " 
  might 
  therefore 
  be 
  both 
  of 
  practical 
  and 
  of 
  theo- 
  

   retical 
  interest. 
  Accordingly 
  the 
  present 
  investigation, 
  which 
  

   has 
  extended 
  over 
  a 
  space 
  of 
  four 
  years, 
  was 
  undertaken 
  to 
  clear 
  

   up, 
  if 
  possible, 
  the 
  discrepancies. 
  

  

  It 
  was 
  found, 
  in 
  verification 
  of 
  the 
  work 
  of 
  Foester 
  and 
  Seidel, 
  

   that 
  copper 
  dissolves 
  in 
  cupric 
  sulphate 
  with 
  the 
  formation 
  of 
  a 
  

   small 
  quantity 
  of 
  cuprous 
  sulphate, 
  which 
  attains 
  a 
  definite 
  

   concentration 
  for 
  each 
  temperature. 
  Unless 
  acid 
  is 
  present, 
  

   cuprous 
  oxide 
  or 
  hydroxide 
  is 
  formed 
  by 
  hydrolysis 
  from 
  this 
  

   sulphate. 
  The 
  consequence 
  of 
  this 
  singular 
  condition 
  of 
  equili- 
  

   brium 
  is 
  that 
  from 
  the 
  pure 
  acidified 
  cupric 
  solution 
  less 
  copper 
  

   is 
  deposited 
  than 
  corresponds 
  with 
  the 
  current 
  of 
  electricity 
  used, 
  

   because 
  some 
  of 
  the 
  copper 
  goes 
  into 
  the 
  formation 
  of 
  cuprous 
  

   sulphate 
  : 
  and 
  from 
  the 
  partly 
  cuprous 
  solutions 
  more 
  copper 
  is 
  

   deposited 
  than 
  corresponds 
  with 
  the 
  current, 
  because 
  in 
  this 
  case 
  

   only 
  single 
  charges 
  of 
  electricity 
  are 
  set 
  free 
  from 
  some 
  of 
  the 
  

   ions 
  deposited. 
  We 
  are 
  thus 
  between 
  Scylla 
  and 
  Charybdis. 
  

  

  Moreover, 
  before 
  the 
  cupric 
  solution 
  is 
  made 
  so 
  dilute 
  that 
  its 
  

   solvent 
  action 
  becomes 
  negligible 
  with 
  a 
  given 
  current 
  density, 
  

   the 
  deposition 
  of 
  hydrogen 
  interferes 
  with 
  the 
  exact 
  determina- 
  

   tion 
  of 
  the 
  electrochemical 
  equivalent, 
  even 
  before 
  the 
  hydrogen 
  

   is 
  actually 
  evolved 
  in 
  bubbles. 
  Hence 
  the 
  use 
  of 
  a 
  small 
  cathode 
  

   is 
  dangerous 
  beyond 
  a 
  limit 
  which 
  depends 
  upon 
  the 
  degree 
  of 
  

   accuracy 
  required. 
  With 
  small 
  current 
  density 
  an 
  approximate 
  

   correction 
  may 
  be 
  made 
  for 
  the 
  area 
  of 
  the 
  cathode. 
  Yanni's 
  

  

  * 
  This 
  Abstract 
  was 
  prepared 
  for 
  this 
  Journal 
  by 
  one 
  of 
  the 
  authors. 
  The 
  

   original 
  paper 
  was 
  presented 
  to 
  the 
  National 
  Academy 
  of 
  Sciences 
  in 
  November 
  ; 
  

   it 
  is 
  printed 
  in 
  full 
  in 
  vol. 
  xxxv 
  of 
  the 
  Proceedings 
  of 
  the 
  American 
  Academy, 
  

   and 
  in 
  vol. 
  xxxii 
  of 
  the 
  Zeitschrift 
  fur 
  physikalische 
  Chemie. 
  

  

  