﻿AS 
  A 
  SOURCE 
  OF 
  THE 
  NITROGEN 
  FOUND 
  IN 
  PLANTS. 
  597 
  

  

  or 
  to 
  deoxidise 
  them. 
  The 
  earliest 
  teachers 
  of 
  this 
  doctrine, 
  Cavendish, 
  Watt, 
  

   Meusnier, 
  and 
  Lavoisier, 
  supposed 
  this 
  deoxidising 
  power 
  to 
  be 
  chiefly 
  expended 
  

   upon 
  water. 
  At 
  a 
  later 
  period, 
  when 
  the 
  fact 
  that 
  carbonic 
  acid 
  is 
  an 
  oxide 
  of 
  

   carbon 
  was 
  discovered, 
  and 
  Priestley's 
  experiments 
  on 
  the 
  conversion 
  of 
  fixed 
  

   air 
  into 
  free 
  oxygen, 
  by 
  the 
  green 
  leaves 
  of 
  plants 
  in 
  the 
  presence 
  of 
  sunshine, 
  

   were 
  recalled, 
  the 
  deoxidising 
  powers 
  of 
  a 
  plant 
  were 
  supposed 
  to 
  be 
  mainly 
  

   expended 
  on 
  carbonic 
  acid. 
  At 
  present, 
  we 
  should 
  decline 
  to 
  say 
  whether 
  this 
  

   acid 
  or 
  water 
  was 
  most 
  the 
  subject 
  of 
  deoxidation 
  in 
  plants 
  ; 
  and 
  we 
  should 
  add 
  

   to 
  those 
  oxides, 
  sulphuric 
  acid, 
  as 
  constantly 
  undergoing 
  separation 
  into 
  its 
  ele- 
  

   ments. 
  To 
  such 
  a 
  conclusion 
  we 
  are 
  driven 
  by 
  the 
  fact, 
  that 
  whilst 
  unoxidised 
  

   sulphur 
  is 
  found 
  in 
  many 
  of 
  the 
  constituents 
  of 
  plants, 
  sulphates 
  are 
  the 
  only 
  

   compounds 
  of 
  sulphur 
  which 
  are 
  found 
  entering 
  them. 
  

  

  Whatever 
  else, 
  however, 
  is 
  doubtful, 
  this 
  is 
  certain, 
  and 
  is 
  acknowledged 
  by 
  

   chemists 
  of 
  every 
  school, 
  viz., 
  that 
  a 
  plant 
  is 
  like 
  a 
  blast-furnace, 
  which 
  the 
  sun 
  

   kindles 
  every 
  day 
  into 
  full 
  action 
  ; 
  and 
  that 
  no 
  oxide 
  can 
  pass 
  through 
  such 
  an 
  

   apparatus, 
  without 
  risking 
  the 
  loss 
  of 
  all 
  its 
  oxygen. 
  With 
  what 
  consistency, 
  

   then, 
  can 
  it 
  be 
  contended, 
  that 
  water, 
  carbonic 
  acid, 
  and 
  sulphuric 
  acid, 
  cannot 
  

   pass 
  through 
  a 
  plant 
  in 
  the 
  presence 
  of 
  sunshine, 
  without 
  being 
  deprived 
  in 
  whole 
  

   or 
  in 
  part 
  of 
  their 
  oxygen, 
  but 
  that 
  the 
  much 
  more 
  easily 
  deoxidised 
  nitric 
  acid, 
  in 
  

   the 
  same 
  circumstances, 
  will 
  not 
  suffer 
  deoxidation 
  ? 
  It 
  might 
  as 
  well 
  be 
  affirmed 
  

   that 
  a 
  blast-furnace 
  may 
  be 
  competent 
  to 
  reduce 
  the 
  refractory 
  oxide 
  of 
  iron, 
  and 
  

   yet 
  be 
  incompetent 
  to 
  reduce 
  the 
  easily 
  reducible 
  oxide 
  of 
  lead. 
  

  

  No 
  one 
  I 
  think 
  will 
  deny, 
  that 
  out 
  of 
  a 
  plant, 
  sulphates 
  are 
  deprived 
  of 
  oxygen 
  

   with 
  much 
  more 
  difficulty 
  than 
  nitrates 
  are 
  ; 
  if, 
  however, 
  the 
  deoxidising 
  force 
  at 
  

   work 
  within 
  a 
  plant 
  can 
  deprive 
  sulphates 
  of 
  their 
  oxygen, 
  a 
  fortiori 
  it 
  can 
  deprive 
  

   nitrates 
  of 
  their 
  oxygen, 
  and 
  we 
  must 
  concede 
  their 
  deoxidability 
  and 
  deoxida- 
  

   tion. 
  

  

  But 
  further, 
  the 
  alkaline 
  nitrates 
  which 
  are 
  the 
  medium 
  of 
  the 
  introduction 
  

   of 
  nitric 
  acid 
  into 
  plants, 
  will 
  certainly 
  within 
  them 
  separate 
  more 
  or 
  less 
  com- 
  

   pletely 
  into 
  acid 
  and 
  alkali, 
  and 
  let 
  the 
  former 
  become 
  free. 
  Those 
  who 
  contend 
  

   that 
  nitrate 
  of 
  soda 
  profits 
  plants 
  only 
  in 
  so 
  far 
  as 
  it 
  contains 
  soda, 
  imply 
  by 
  this 
  

   statement 
  that 
  the 
  nitric 
  acid 
  is 
  set 
  free 
  from 
  the 
  soda, 
  and 
  in 
  some 
  way 
  disposed 
  of. 
  

   All 
  chemists, 
  moreover, 
  will 
  acknowledge 
  that 
  the 
  large 
  amount 
  of 
  fixed 
  alkaline 
  

   bases 
  found 
  present 
  in 
  every 
  plant 
  in 
  union 
  with 
  organic 
  acids, 
  compels 
  us, 
  what- 
  

   ever 
  theory 
  we 
  hold, 
  to 
  look 
  upon 
  these 
  acids 
  developed 
  within 
  the 
  plant, 
  as 
  having 
  

   taken 
  the 
  place 
  of 
  the 
  inorganic 
  or 
  mineral 
  acids 
  which 
  accompanied 
  the 
  bases 
  into 
  

   its 
  structure. 
  Nitric 
  acid 
  must 
  therefore 
  be 
  often 
  set 
  free 
  within 
  vegetable 
  organ- 
  

   isms 
  ; 
  and 
  when 
  set 
  free, 
  must 
  more 
  rapidly 
  than 
  any 
  uncombined 
  inorganic 
  oxide 
  

   which 
  is 
  present 
  in 
  plants, 
  suffer 
  instant 
  deoxidation. 
  This 
  proposition, 
  I 
  think, 
  

   needs 
  no 
  proof. 
  Uncombined 
  carbonic 
  or 
  sulphuric 
  acid, 
  cannot 
  be 
  deoxidised 
  by 
  

   any 
  known 
  artificial 
  process, 
  so 
  as 
  to 
  separate 
  its 
  oxygen 
  as 
  free 
  gas. 
  Water 
  can 
  

   be 
  made 
  to 
  yield 
  free 
  oxygen 
  only 
  by 
  a 
  powerful 
  voltaic 
  current, 
  — 
  by 
  an 
  intense 
  

  

  