﻿Studies 
  of 
  Photo-synthesis 
  in 
  Fresh-water 
  Algm. 
  207 
  

  

  over 
  which 
  is 
  placed 
  a 
  flat 
  rubber 
  band 
  ; 
  on 
  this 
  is 
  placed 
  the 
  glass 
  cover, 
  

   provided 
  with 
  a 
  flat 
  flange 
  to 
  come 
  in 
  apposition. 
  An 
  air-tight 
  union 
  is 
  

   obtained 
  by 
  means 
  of 
  a 
  metal 
  screw-top 
  working 
  on 
  a 
  glass 
  screw-thread 
  

   moulded 
  on 
  the 
  outside 
  of 
  the 
  wide 
  neck 
  of 
  the 
  jar. 
  It 
  was 
  hence 
  

   possible 
  to 
  keep 
  certain 
  of 
  the 
  jars 
  in 
  connection 
  with 
  the 
  atmosphere 
  by 
  

   merely 
  covering 
  with 
  a 
  tied-on 
  cap 
  of 
  lawn, 
  and 
  in 
  others 
  to 
  screw 
  down 
  the 
  

   lids 
  and 
  shut 
  off 
  access 
  to 
  the 
  atmosphere. 
  Each 
  jar 
  received 
  200 
  c.c. 
  of 
  

   tap-water, 
  the 
  supply 
  being 
  Eickmansworth 
  water. 
  This 
  is 
  a 
  surface 
  water 
  

   containing 
  a 
  small 
  amount 
  of 
  calcium 
  salts, 
  but 
  otherwise 
  a 
  pure, 
  good 
  water. 
  

  

  Each 
  jar 
  was 
  next 
  inseminated 
  with 
  2 
  c.c. 
  of 
  a 
  dilute 
  stirred 
  up 
  suspension 
  

   in 
  water 
  of 
  an 
  algal 
  growth 
  which 
  had 
  been 
  developed 
  by 
  self-growth 
  in 
  a 
  

   small 
  muslin-covered 
  jar 
  on 
  the 
  west 
  window. 
  The 
  amount 
  of 
  nitrogen 
  

   introduced 
  in 
  this 
  insemination 
  was 
  infinitesimal, 
  and, 
  in 
  any 
  case, 
  its 
  

   amount, 
  as 
  well 
  as 
  any 
  trace 
  in 
  the 
  200 
  c.c. 
  of 
  tap-water, 
  can 
  be 
  accounted 
  

   for 
  by 
  deducting 
  the 
  average 
  small 
  amounts 
  of 
  nitrogen 
  found 
  in 
  jSTos. 
  1, 
  3, 
  

   and 
  4, 
  which 
  really 
  serve 
  as 
  controls, 
  the 
  net 
  increases 
  in 
  the 
  others 
  then 
  

   show 
  the 
  favouring 
  action 
  on 
  nitrogen 
  fixation 
  of 
  the 
  various 
  procedures. 
  

   After 
  the 
  addition 
  of 
  the 
  200 
  c.c. 
  of 
  tap-water 
  and 
  the 
  2 
  c.c. 
  of 
  algal, 
  

   suspension 
  in 
  all 
  twelve 
  cases, 
  each 
  was 
  next 
  treated 
  as 
  noted 
  in 
  the 
  

   schedule 
  below, 
  and 
  afterwards 
  they 
  were 
  either 
  kept 
  closed 
  with 
  glass 
  lids 
  

   screwed 
  down, 
  or 
  covered 
  with 
  fine 
  lawn 
  only, 
  and 
  were 
  kept 
  in 
  light 
  or 
  

   darkness 
  as 
  noted. 
  Darkness 
  was 
  secured 
  in 
  a 
  wooden 
  shed 
  close 
  alongside. 
  

   Light 
  meant 
  full 
  exposure 
  to 
  daylight, 
  on 
  the 
  middle 
  of 
  the 
  grass 
  lawn, 
  

   except 
  at 
  mid-day 
  in 
  the 
  hot 
  weather, 
  when 
  a 
  muslin 
  shade 
  was 
  thrown 
  over, 
  

   and 
  tin 
  sheets 
  placed 
  loosely 
  on 
  top 
  to 
  protect 
  from 
  excessive 
  light 
  and 
  heat, 
  

   which 
  are 
  fatal 
  to 
  alga?. 
  

  

  In 
  order 
  to 
  save 
  space 
  in 
  tabulation 
  the 
  amounts 
  of 
  nitrogen 
  found 
  by 
  the 
  

   Kjeldahl 
  determination 
  carried 
  out 
  at 
  the 
  conclusion 
  of 
  the 
  experiments 
  are 
  

   here 
  placed 
  opposite 
  the 
  description 
  of 
  the 
  treatment 
  of 
  each 
  jar 
  : 
  — 
  

  

  No. 
  1. 
  — 
  Tap-water 
  and 
  algae 
  only, 
  glass 
  lid 
  screwed 
  down, 
  kept 
  in 
  light. 
  

   Nitrogen 
  = 
  0*3 
  mgrm. 
  

  

  No. 
  2. 
  — 
  Tap-water 
  and 
  algae 
  only, 
  no 
  glass 
  lid, 
  top 
  covered 
  by 
  fine 
  lawn, 
  

   kept 
  in 
  light. 
  Nitrogen 
  = 
  1*6 
  mgrm. 
  

  

  No. 
  3. 
  — 
  Tap-water 
  and 
  algae 
  only, 
  screwed 
  down, 
  no 
  glass 
  lid, 
  kept 
  in 
  

   darkness. 
  Nitrogen 
  = 
  01 
  mgrm. 
  

  

  No. 
  4. 
  — 
  Tap-water 
  and 
  algae 
  only, 
  covered 
  by 
  fine 
  lawn, 
  kept 
  in 
  darkness. 
  

   Nitrogen 
  = 
  0'3 
  mgrm. 
  

  

  No. 
  5. 
  — 
  Tap- 
  water, 
  algae, 
  2 
  c.c. 
  of 
  5 
  per 
  cent. 
  Na 
  2 
  HP0 
  4 
  ,12H 
  2 
  (i.e., 
  

   0*05 
  per 
  cent, 
  of 
  Na 
  2 
  HP0 
  4 
  ,12H 
  2 
  0) 
  lawn 
  cover 
  only, 
  kept 
  in 
  light. 
  

   Nitrogen 
  = 
  8 
  - 
  l 
  mgrm. 
  

  

  