﻿68 
  JOURNAL 
  OF 
  THE 
  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  VOL. 
  12, 
  NO. 
  3 
  

  

  change 
  in 
  volume. 
  If 
  E 
  denotes 
  the 
  open 
  circuit 
  voltage 
  of 
  the 
  cell 
  

   W 
  equals 
  96500 
  E 
  volt-coulombs- 
  for 
  1 
  equivalent. 
  Q 
  expressed 
  in 
  

   calories 
  may 
  be 
  converted 
  to 
  voltcoulombs 
  by 
  multiplying 
  by 
  4.183 
  

   and 
  the 
  equation 
  becomes: 
  

  

  dE 
  1 
  

  

  — 
  = 
  - 
  (E- 
  0.000021674 
  Q). 
  (2) 
  

  

  Both 
  E 
  and 
  Q 
  are 
  dependent 
  on 
  the 
  concentration 
  of 
  the 
  electrolyte 
  

   which 
  for 
  this 
  experiment 
  was 
  of 
  1.280 
  sp. 
  gr. 
  The 
  value 
  of 
  E 
  cor- 
  

   responding 
  to 
  the 
  initial 
  value 
  T 
  was 
  observed 
  directly. 
  The 
  value 
  

   for 
  Q 
  may 
  be 
  calculated 
  from 
  published 
  thermochemical 
  data. 
  

  

  The 
  commonly 
  accepted 
  reaction 
  of 
  the 
  lead 
  accumulator 
  during 
  

   discharge 
  may 
  be 
  described 
  by 
  the 
  following 
  equation: 
  

  

  Positive 
  plate, 
  Pb02+H2S04 
  

  

  +W.H2O 
  -^ 
  2PbS04+(n+2)H20 
  

   Negative 
  plate, 
  Pb+H2S04 
  J 
  

  

  where 
  n 
  is 
  the 
  number 
  of 
  molecules 
  of 
  water 
  to 
  2 
  molecules 
  of 
  sulphuric 
  

   acid 
  in 
  the 
  original 
  solution. 
  The 
  corresponding 
  thermochemical 
  

   equation 
  is 
  

  

  PbOo 
  + 
  Pb 
  + 
  2H2SO4 
  + 
  W.H2O 
  = 
  2PbS04 
  + 
  (w 
  + 
  2)H20 
  + 
  Q„ 
  

   where 
  Q„, 
  the 
  heat 
  of 
  the 
  reaction, 
  depends 
  on 
  the 
  dilution 
  of 
  the 
  

   acid, 
  which 
  is 
  fixed 
  by 
  n. 
  Since 
  the 
  chemical 
  reaction 
  must 
  take 
  

   H2SO4 
  from 
  the 
  dilute 
  electrolyte, 
  the 
  energy 
  represented 
  by 
  Q„ 
  for 
  

   other 
  strengths 
  of 
  acid 
  will 
  be 
  less 
  in 
  amount 
  by 
  the 
  quantity 
  of 
  heat 
  

   evolved 
  by 
  dilution 
  of 
  the 
  acid, 
  or 
  Q„ 
  will 
  be 
  greater 
  if 
  the 
  concen- 
  

   tration 
  is 
  greater. 
  

  

  Values 
  for 
  Q 
  have 
  been 
  determined 
  by 
  Streinz^ 
  and 
  Tscheltzow^ 
  to 
  

   be 
  87000 
  and 
  88600 
  calories, 
  respectively. 
  The 
  mean 
  of 
  their 
  determi- 
  

   nations 
  is 
  87800 
  calories. 
  Dolezalek^ 
  states 
  that 
  these 
  values 
  apply 
  

   to 
  dilute 
  sulphuric 
  acid 
  (1 
  molecule 
  of 
  H2SO4 
  to 
  about 
  400 
  molecules 
  

   of 
  H2O) 
  and 
  hence 
  a 
  correction 
  for 
  the 
  heat 
  of 
  dilution 
  is 
  necessary. 
  

   The 
  heat 
  of 
  dilution^ 
  of 
  the 
  acid 
  solution 
  from 
  a 
  specific 
  gravity 
  of 
  

   1.280 
  as 
  used 
  in 
  our 
  experiment 
  to 
  the 
  concentration 
  equivalent 
  to 
  

   1 
  molecule 
  of 
  acid 
  to 
  399 
  mols.of 
  water 
  is 
  2210 
  calories 
  per 
  gram 
  mole- 
  

   cule. 
  Two 
  gram 
  molecules 
  are 
  involved 
  and 
  hence 
  the 
  value 
  for 
  

  

  2 
  The 
  value 
  96500 
  coulombs 
  is 
  based 
  on 
  recent 
  determinations 
  with 
  the 
  silver 
  and 
  iodine 
  

   voltameters 
  by 
  Vinal 
  and 
  Bates 
  at 
  the 
  Bureau 
  of 
  Standards 
  Sci. 
  Paper 
  No. 
  218. 
  

   3Wied. 
  Ann. 
  53: 
  698. 
  1894. 
  

  

  * 
  Comptes 
  Rendus 
  100: 
  1458. 
  1885. 
  

  

  * 
  Theory 
  of 
  the 
  Lead 
  Accumulator, 
  p. 
  29. 
  

  

  ' 
  Thomsen's 
  data, 
  Landolt 
  and 
  Bornstein 
  tables, 
  ed. 
  4, 
  p. 
  885. 
  

  

  