﻿PHOTOSYNTHESIS 
  BALY 
  241 
  

  

  One 
  of 
  the 
  greatest 
  difficulties 
  met 
  with 
  in 
  this 
  work 
  was 
  the 
  

   preparation 
  of 
  the 
  various 
  materials 
  used 
  for 
  the 
  surfaces, 
  since 
  it 
  is 
  

   absolutely 
  essential 
  that 
  these 
  be 
  completely 
  free 
  from 
  any 
  trace 
  of 
  

   alkali. 
  It 
  is 
  well 
  known 
  that 
  when 
  metalhc 
  hydroxides 
  and 
  carbon- 
  

   ates 
  are 
  precipitated 
  they 
  tend 
  to 
  absorb 
  the 
  alkali, 
  and 
  the 
  removal 
  

   of 
  this 
  is 
  extraordinarily 
  troublesome. 
  The 
  absence 
  of 
  any 
  alkaline 
  

   reaction 
  in 
  the 
  filtrate 
  after 
  the 
  powder 
  has 
  been 
  boiled 
  with 
  water 
  

   is 
  no 
  criterion 
  of 
  purity, 
  and 
  the 
  only 
  satisfactory 
  method 
  is 
  to 
  pass 
  

   carbon 
  dioxide 
  into 
  a 
  suspension 
  of 
  the 
  powder 
  in 
  water 
  for 
  two 
  

   hours 
  in 
  the 
  dark, 
  and 
  the 
  filtrate 
  after 
  concentration 
  must 
  yield 
  no 
  

   weighable 
  quantity 
  of 
  alkaline 
  carbonate. 
  

  

  It 
  was 
  frequently 
  found 
  that 
  the 
  carbonates 
  of 
  nickel 
  and 
  cobalt, 
  

   even 
  when 
  completely 
  freed 
  from 
  alkali, 
  were 
  entirely 
  ineffective 
  in 
  

   promoting 
  photosynthesis. 
  These 
  can, 
  however, 
  be 
  activated 
  either 
  

   by 
  heating 
  to 
  120° 
  or 
  by 
  exposure 
  in 
  thin 
  layers 
  to 
  ultra-violet 
  light, 
  

   and 
  this 
  fact 
  afforded 
  a 
  very 
  convincing 
  method 
  of 
  carrying 
  out 
  

   controls. 
  A 
  quantity 
  of 
  one 
  of 
  these 
  inactive 
  powders 
  gives 
  no 
  trace 
  

   of 
  carbohydrates 
  when 
  exposed 
  to 
  visible 
  light 
  in 
  the 
  manner 
  de- 
  

   scribed. 
  The 
  same 
  sample 
  of 
  powder 
  when 
  activated 
  and 
  used 
  in 
  

   the 
  same 
  apparatus, 
  with 
  the 
  same 
  water, 
  the 
  same 
  light, 
  and 
  carbon 
  

   dioxide 
  from 
  the 
  same 
  source, 
  gives 
  a 
  good 
  yield 
  of 
  carbohydrates. 
  

   So, 
  once 
  and 
  for 
  all, 
  is 
  all 
  doubt 
  removed 
  as 
  to 
  the 
  possible 
  effect 
  

   of 
  impurities. 
  

  

  For 
  the 
  benefit 
  of 
  those 
  who 
  may 
  wish 
  to 
  repeat 
  these 
  experiments, 
  

   it 
  may 
  be 
  stated 
  that 
  more 
  recently 
  it 
  has 
  been 
  found 
  possible 
  to 
  

   prepare 
  nickel 
  carbonate 
  by 
  a 
  new 
  method 
  which 
  is 
  free 
  from 
  the 
  

   objections 
  characteristic 
  of 
  its 
  precipitation 
  by 
  means 
  of 
  alkali 
  

   carbonate. 
  A 
  solution 
  of 
  carbonic 
  acid 
  in 
  conductivity 
  water 
  is 
  

   electrolyzed, 
  the 
  electrodes 
  being 
  made 
  of 
  nickel 
  plates. 
  The 
  current 
  

   is 
  taken 
  from 
  a 
  220-volt 
  circuit, 
  and 
  sufficient 
  resistance 
  is 
  intercalated 
  

   to 
  reduce 
  the 
  current 
  density 
  to 
  from 
  1 
  or 
  2 
  amperes 
  per 
  square 
  

   decimeter. 
  The 
  electrolyte 
  is 
  cooled 
  by 
  glass 
  coils 
  through 
  which 
  a 
  

   stream 
  of 
  water 
  is 
  maintained. 
  With 
  electrodes 
  190 
  square 
  centi- 
  

   meters 
  in 
  area 
  it 
  is 
  possible 
  to 
  prepare 
  30 
  grams 
  of 
  pure 
  carbonate 
  in 
  

   24 
  hours. 
  The 
  carbonate 
  should 
  be 
  collected 
  every 
  day 
  by 
  filtration, 
  

   and 
  it 
  is 
  advisable 
  to 
  clean 
  the 
  electrodes 
  with 
  emery 
  paper 
  every 
  

   third 
  day. 
  

  

  To 
  sum 
  up 
  the 
  results, 
  so 
  far 
  as 
  they 
  have 
  been 
  described, 
  it 
  has 
  

   been 
  found 
  possible 
  in 
  the 
  laboratory 
  to 
  produce 
  carbohydrates 
  

   directly 
  from 
  carbonic 
  acid 
  by 
  a 
  process 
  which 
  is 
  physically 
  similar 
  

   to 
  that 
  of 
  the 
  living 
  plant. 
  The 
  essential 
  difficulty 
  in 
  our 
  under- 
  

   standing 
  of 
  the 
  natural 
  photosynthesis 
  has 
  been 
  solved, 
  namely 
  the 
  

   use 
  of 
  visible 
  light 
  as 
  the 
  agent 
  in 
  a 
  process 
  which 
  the 
  elementary 
  

   laws 
  of 
  photochemistry 
  taught 
  us 
  to 
  believe 
  could 
  only 
  be 
  achieved 
  

  

  