﻿FEB. 
  4, 
  1922 
  VINAL 
  AND 
  ALTRUP: 
  CELLS 
  AT 
  LOW 
  TEMPERATURES 
  

  

  67 
  

  

  Silver 
  chloride 
  dry 
  cells 
  were 
  measured 
  in 
  a 
  similar 
  manner, 
  and 
  the 
  

   open 
  circuit 
  voltages 
  are 
  given 
  in 
  Table 
  1. 
  When 
  the 
  voltage 
  was 
  

   measured 
  by 
  the 
  25,000-ohm 
  voltmeter, 
  however, 
  the 
  terminal 
  voltage 
  

   began 
  to 
  fall 
  rapidly 
  fromO° 
  C. 
  downward. 
  At 
  —10° 
  it 
  was 
  0.9 
  volt, 
  

   and 
  from 
  this 
  point 
  it 
  decreased 
  nearly 
  linearly 
  to 
  0.05 
  volt 
  at 
  —50°. 
  

  

  Experiments 
  were 
  also 
  made 
  to 
  determine 
  the 
  voltage 
  of 
  storage 
  

   cells 
  within 
  the 
  range 
  +25° 
  to 
  —72° 
  C, 
  using 
  the 
  electrometer, 
  the 
  

   potentiometer 
  and 
  the 
  voltmeter 
  to 
  measure 
  the 
  voltage. 
  As 
  freezing 
  

   did 
  not 
  occur 
  within 
  this 
  range, 
  the 
  potentiometer 
  gave 
  the 
  most 
  ac- 
  

   curate 
  results 
  and 
  these 
  are 
  given 
  in 
  Table 
  1, 
  but 
  the 
  results 
  of 
  all 
  

  

  TABLE 
  1. 
  

   Open 
  Circuit 
  Voltages 
  of 
  Cells 
  for 
  Values 
  Below 
  —70° 
  C. 
  See 
  Fig. 
  2 
  

  

  * 
  Based 
  on 
  potentiometer 
  readings. 
  

  

  ** 
  Interpolated 
  values 
  based 
  on 
  electrometer 
  readings. 
  

  

  methods 
  were 
  in 
  good 
  agreement. 
  The 
  temperature 
  coefficient 
  was 
  

   small 
  and 
  constant. 
  This 
  fact 
  permitted 
  an 
  accurate 
  estimate 
  of 
  

   the 
  temperature 
  coefficient 
  to 
  be 
  made 
  since 
  the 
  cell 
  had 
  sufficient 
  

   time 
  for 
  thermal 
  equilibrium 
  to 
  be 
  established 
  at 
  the 
  beginning 
  and 
  

   end 
  of 
  this 
  range. 
  The 
  temperature 
  coefficient 
  was 
  found 
  to 
  be 
  

   0.000398 
  volt 
  per 
  degree 
  C. 
  

  

  It 
  is 
  interesting 
  to 
  compare 
  this 
  result 
  with 
  the 
  value 
  computed 
  from 
  

   the 
  available 
  thermochemical 
  data 
  and 
  the 
  Gibbs-Helmholtz 
  equation. 
  

   This 
  equation 
  is 
  usually 
  written 
  

  

  2=^-T«^ 
  (1) 
  

  

  where 
  Q 
  is 
  the 
  heat 
  of 
  the 
  reaction; 
  W 
  the 
  available 
  work 
  and 
  T 
  the 
  

   absolute 
  temperature. 
  This 
  equation 
  is 
  applicable 
  to 
  a 
  reversible 
  

   cell 
  in 
  which 
  the 
  passage 
  of 
  current 
  does 
  not 
  involve 
  any 
  appreciable 
  

  

  