﻿Chemistry 
  and 
  Physics. 
  317 
  

  

  The 
  kathode 
  on 
  which 
  the 
  silver 
  is 
  to 
  be 
  deposited 
  shall 
  take 
  

   the 
  form 
  of 
  a 
  platinum 
  bowl 
  not 
  less 
  than 
  10 
  centimeters 
  in 
  diame- 
  

   ter, 
  and 
  from 
  4 
  to 
  5 
  centimeters 
  in 
  depth. 
  

  

  The 
  anode 
  shall 
  be 
  a 
  disc 
  or 
  plate 
  of 
  pure 
  silver 
  some 
  30 
  square 
  

   centimeters 
  in 
  area 
  and 
  2 
  or 
  3 
  millimeters 
  in 
  thickness. 
  

  

  This 
  shall 
  be 
  supported 
  horizontally 
  in 
  the 
  liquid 
  near 
  the 
  top 
  

   of 
  the 
  solution 
  by 
  a 
  silver 
  rod 
  riveted 
  through 
  its 
  center. 
  To 
  

   prevent 
  the 
  disintegrated 
  silver 
  which 
  is 
  formed 
  on 
  the 
  anode 
  

   from 
  falling 
  upon 
  the 
  kathode, 
  the 
  anode 
  shall 
  be 
  wrapped 
  

   around 
  with 
  pure 
  filter 
  paper, 
  secured 
  at 
  the 
  back 
  by 
  suitable 
  

   folding. 
  

  

  The 
  liquid 
  shall 
  consist 
  of 
  a 
  neutral 
  solution 
  of 
  pure 
  silver 
  

   nitrate, 
  containing 
  about 
  15 
  parts 
  by 
  weight 
  of 
  the 
  nitrate 
  to 
  85 
  

   parts 
  of 
  water. 
  

  

  The 
  resistance 
  of 
  the 
  voltameter 
  changes 
  somewhat 
  as 
  the 
  cur- 
  

   rent 
  passes. 
  To 
  prevent 
  these 
  changes 
  having 
  too 
  great 
  an 
  effect 
  

   on 
  the 
  current, 
  some 
  resistance 
  besides 
  that 
  of 
  the 
  voltameter 
  

   should 
  be 
  inserted 
  in 
  the 
  circuit. 
  The 
  total 
  metallic 
  resistance 
  of 
  

   the 
  circuit 
  should 
  not 
  be 
  less 
  than 
  10 
  ohms. 
  

  

  Method 
  of 
  Making 
  a 
  Measurement. 
  The 
  platinum 
  bowl 
  is 
  to 
  

   be 
  washed 
  consecutively 
  with 
  nitric 
  acid, 
  distilled 
  water 
  and 
  

   absolute 
  alcohol 
  ; 
  it 
  is 
  then 
  to 
  be 
  dried 
  at 
  160° 
  C, 
  and 
  left 
  to 
  

   cool 
  in 
  a 
  desiccator. 
  When 
  thoroughly 
  cool 
  it 
  is 
  to 
  be 
  weighed 
  

   carefully. 
  

  

  It 
  is 
  to 
  be 
  nearly 
  filled 
  with 
  the 
  solution 
  and 
  connected 
  to 
  the 
  

   rest 
  of 
  the 
  circuit 
  by 
  being 
  placed 
  on 
  a 
  clean 
  insulated 
  copper 
  

   support 
  to 
  which 
  a 
  binding 
  screw 
  is 
  attached. 
  

  

  The 
  anode 
  is 
  then 
  to 
  be 
  immersed 
  in 
  the 
  solution 
  so 
  as 
  to 
  be 
  

   well 
  covered 
  by 
  it 
  and 
  supported 
  in 
  that 
  position; 
  the 
  connec- 
  

   tions 
  to 
  the 
  rest 
  of 
  the 
  circuit 
  are 
  then 
  to 
  be 
  made. 
  

  

  Contact 
  is 
  to 
  be 
  made 
  at 
  the 
  key, 
  noting 
  the 
  time. 
  The 
  cur- 
  

   rent 
  is 
  to 
  be 
  allowed 
  to 
  pass 
  for 
  not 
  less 
  than 
  halt 
  an 
  hour, 
  and 
  

   the 
  time 
  of 
  breaking 
  contact 
  observed. 
  

  

  The 
  solution 
  is 
  now 
  to 
  be 
  removed 
  from 
  the 
  bowl 
  and 
  the 
  

   deposit 
  washed 
  with 
  distilled 
  water 
  and 
  left 
  to 
  soak 
  for 
  at 
  least 
  

   six 
  hours. 
  It 
  i^ 
  then 
  to 
  be 
  rinsed 
  successively 
  with 
  distilled 
  

   water 
  and 
  absolute 
  alcohol 
  and 
  dried 
  in 
  a 
  hot-air 
  bath 
  at 
  a 
  tem- 
  

   perature 
  of 
  about 
  160° 
  C. 
  Alter 
  cooling 
  in 
  a 
  desiccator 
  it 
  is 
  to 
  

   be 
  weighed 
  again. 
  The 
  gain 
  in 
  mass 
  gives 
  the 
  silver 
  deposited. 
  

  

  To 
  find 
  the 
  time 
  average 
  of 
  the 
  current 
  in 
  amperes, 
  this 
  mass, 
  

   expressed 
  in 
  grams, 
  must 
  be 
  divided 
  by 
  the 
  number 
  of 
  seconds 
  

   during 
  which 
  the 
  current 
  has 
  passed 
  and 
  by 
  0*001118. 
  

  

  In 
  determining 
  the 
  constant 
  of 
  an 
  instrument 
  by 
  this 
  method, 
  

   the 
  current 
  should 
  be 
  kept 
  as 
  nearly 
  uniform 
  as 
  possible 
  and 
  the 
  

   readings 
  of 
  the 
  instrument 
  observed 
  at 
  frequent 
  intervals 
  of 
  time. 
  

   These 
  observations 
  give 
  a 
  curve 
  from 
  which 
  the 
  reading 
  corre- 
  

   sponding 
  to 
  the 
  mean 
  current 
  (time-average 
  of 
  the 
  current) 
  can 
  

   be 
  found. 
  The 
  current, 
  as 
  calculated 
  from 
  the 
  voltameter 
  results, 
  

   corresponds 
  to 
  this 
  reading. 
  

  

  