﻿Studies 
  of 
  Photo- 
  synthesis 
  in 
  Fresh-water 
  Algce. 
  205 
  

  

  In 
  order 
  to 
  obtain 
  as 
  pure 
  air 
  as 
  possible, 
  the 
  exposures 
  and 
  growths 
  were 
  

   made 
  in 
  the 
  open 
  air 
  at 
  Heron's 
  Lodge, 
  Heronsgate, 
  Chorley 
  Wood, 
  Herts. 
  

   The 
  house 
  is 
  about 
  1£ 
  miles 
  from 
  the 
  railway 
  line, 
  stands 
  on 
  high 
  ground 
  at 
  

   an 
  elevation 
  of 
  about 
  400 
  feet, 
  and 
  possesses 
  a 
  large 
  lawn, 
  in 
  the 
  middle 
  of 
  

   which 
  all 
  the 
  experiments, 
  except 
  the 
  first, 
  were 
  made. 
  The 
  air 
  was 
  tested 
  

   daily 
  for 
  nitrites 
  by 
  starch 
  and 
  potassium 
  iodide 
  papers, 
  and 
  nitrites 
  were 
  

   nearly 
  always 
  present. 
  At 
  the 
  conclusion 
  of 
  the 
  experiments, 
  the 
  growths 
  

   and 
  waters 
  were 
  taken 
  to 
  the 
  laboratory 
  of 
  the 
  Department, 
  then 
  situated 
  

   at 
  the 
  Lister 
  Institute, 
  and 
  there 
  analysed 
  for 
  content 
  of 
  nitrogen 
  by 
  the 
  

   Kjeldahl 
  method. 
  The 
  experiments 
  were 
  made 
  in 
  the 
  spring 
  and 
  summer 
  

   of 
  1918, 
  in 
  the 
  months 
  of 
  April 
  to 
  August 
  inclusive. 
  

  

  Eocperiment 
  1. 
  — 
  Commenced 
  April 
  15, 
  finished 
  August 
  5. 
  We 
  took 
  two 
  

   clear 
  glass 
  flasks 
  of 
  Jena 
  glass, 
  each 
  of 
  1000 
  c.c. 
  capacity, 
  and 
  provided 
  with 
  

   ground 
  glass 
  stoppers. 
  These 
  were 
  almost 
  completely 
  filled 
  with 
  water 
  from 
  

   a 
  clear 
  stream 
  near 
  the 
  house. 
  One 
  was 
  filled 
  up 
  to 
  the 
  glass 
  stopper, 
  and 
  

   then 
  the 
  stopper 
  was 
  inserted, 
  so 
  that 
  the 
  contents 
  of 
  the 
  flask 
  were 
  completely 
  

   shut 
  off 
  from 
  the 
  air. 
  The 
  other 
  flask 
  was 
  filled 
  so 
  that 
  the 
  water 
  stood 
  in 
  

   its 
  neck 
  about 
  4 
  cm. 
  from 
  the 
  top 
  ; 
  the 
  glass 
  stopper 
  was 
  not 
  inserted, 
  but 
  

   instead 
  a 
  loose 
  plug 
  of 
  cotton-wool 
  was 
  used. 
  Over 
  this 
  a 
  piece 
  of 
  fine 
  muslin 
  

   was 
  placed 
  and 
  tied 
  round 
  the 
  neck 
  of 
  the 
  flask 
  with 
  thread 
  ; 
  air, 
  accordingly, 
  

   had 
  access 
  to 
  the 
  contents 
  of 
  this 
  flask. 
  The 
  glass-stoppered 
  flask 
  is 
  a 
  control 
  

   to 
  give 
  the 
  amount 
  of 
  nitrogen 
  present 
  at 
  the 
  outset 
  plus 
  any 
  that 
  can 
  

   possibly 
  be 
  formed 
  in 
  absence 
  of 
  air. 
  

  

  The 
  two 
  flasks 
  were 
  placed 
  outside 
  on 
  the 
  ledge 
  of 
  a 
  first-floor 
  window, 
  

   facing 
  almost 
  due 
  west, 
  so 
  that 
  direct 
  sunlight 
  was 
  only 
  obtained 
  for 
  a 
  few 
  

   hours 
  in 
  the 
  afternoon. 
  Care 
  was 
  taken 
  to 
  give 
  equal 
  chances 
  to 
  the 
  two 
  

   flasks 
  by 
  reversing 
  their 
  positions 
  on 
  the 
  ledge 
  every 
  two 
  or 
  three 
  days. 
  Also 
  

   a 
  small 
  beaker 
  was 
  inverted 
  over 
  the 
  cotton-wool, 
  to 
  prevent 
  contamination 
  

   by 
  rain. 
  The 
  flasks 
  were 
  not 
  inseminated 
  with 
  any 
  organism, 
  but 
  left 
  to 
  

   develop 
  their 
  crops 
  naturally. 
  

  

  On 
  May 
  2 
  a 
  distinct 
  green 
  growth 
  appeared 
  in 
  both 
  flasks, 
  slightly 
  greater 
  

   in 
  the 
  glass-stoppered 
  one. 
  On 
  May 
  7 
  the 
  open 
  flask 
  shows 
  a 
  distinctly 
  

   greater 
  growth 
  than 
  the 
  stoppered 
  one. 
  In 
  direct 
  sunlight 
  bubbles 
  of 
  gas 
  

   are 
  evolved 
  from 
  both, 
  but 
  most 
  from 
  the 
  open 
  flask. 
  May 
  14. 
  — 
  Growth 
  in 
  

   the 
  stoppered 
  flask 
  has 
  stopped, 
  no 
  gas 
  bubbles 
  are 
  given 
  off 
  in 
  sunlight, 
  but 
  

   there 
  is 
  a 
  brisk 
  effervescence 
  in 
  the 
  open 
  flask, 
  and 
  the 
  growth 
  is 
  obviously 
  

   increasing. 
  May 
  20. 
  — 
  All 
  growth 
  is 
  stopped 
  in 
  the 
  closed 
  flask, 
  and 
  the 
  

   growth 
  has 
  turned 
  brown 
  and 
  flocculent. 
  But 
  the 
  growth 
  in 
  the 
  open 
  flask 
  

   is 
  healthy 
  and 
  increasing, 
  and 
  gives 
  off 
  bubbles 
  in 
  sunlight. 
  Frequent 
  

   observations 
  were 
  taken 
  till 
  the 
  conclusion 
  on 
  August 
  5, 
  but 
  for 
  brevity 
  

  

  