and  Subsoils  of  some  of  the  Fields  at  Rothamsted.  333 
soil  when  dried  is  further  pulverised  ; all  stones  retained  bv  a 
sieve  with  ^-inch  meshes  are  removed,  and  all  visible  roots  ; the 
remaining  soil  is  then  finely  powdered,  and  stored  in  bottles  for 
analysis.  The  stones,  roots,  and  fine  soil  obtained  from  the 
original  sample  are  all  weighed. 
The  immediate  drying  of  the  soil  is  absolutely  necessary,  if 
it  is  desired  to  ascertain  the  quantity  of  nitrates  present  in  the 
land  from  which  the  sample  was  taken,  as  the  production  of 
nitrates  takes  place  with  considerable  rapidity  in  a moist  soil 
freely  exposed  to  air.  The  soil  must  not,  however,  be  dried  at 
too  high  a temperature,  or  loss  of  nitrates  may  occur.* 
To  ascertain  the  quantity  of  nitrates  present  in  the  soil, 
200  to  400  grams  of  the  finely-powdered  soil  are  extracted 
with  water  on  a vacuum  filter.  The  nitric  acid  is  determined 
in  the  watery  extract  by  a modification  of  Schloesing’s  method, 
the  details  of  which  have  been  described  elsewhere,  f 
History  of  the  Soils  Examined. 
It  will  be  convenient  to  bring  together  under  one  head  the 
necessary  descriptions  of  the  various  soils  in  which  nitric  acid 
has  been  determined.  All  the  fields  we  have  to  mention  form 
part  of  the  Rothamsted  Farm.  The  soil  is  in  every  case  a 
more  or  less  heavy  loam,  with  flints ; having  a deep  clay 
subsoil,  resting  on  chalk.  In  one  instance  only  was  the  chalk 
reached  at  the  depth  of  6 feet.  Samples  were  in  every  case 
taken  from  several  places  in  the  field  or  plot,  and  the  analyses 
made  on  mixtures  of  these  samples. 
Little  Hoos  Field. — Sampled  September  26-29,  1877.  This 
field  is  not  part  of  the  strictly  experimental  land.  In  1877  the 
crop  was  barley,  in  half  of  which  clover  had  been  sown.  The 
division  of  the  field  we  are  here  concerned  with  had  grown 
cereal  crops  for  eleven  years,  the  last  nine  crops  being  barley. 
During  the  last  seven  years  the  annual  manuring  consisted  of 
superphosphate,  with  2 or  2£  cwts.  of  nitrate  of  sodium. 
Samples  of  soil  were  taken  in  four  places  from  each  division 
of  the  field  ; the  sampling  was  carried  to  the  depth  of  54 
inches. 
Agdell  Field. — Sampled  September  2T-25,  1878,  and  Sep- 
tember 8,  1882.  In  this  field  systematic  experiments  upon 
the  ordinary  four-course  rotation  have  been  conducted  since 
1848.  We  are  only  here  concerned  with  two  divisions  of  the 
field,  representing  respectively  the  highest  and  lowest  condition 
* 1 Trans.  Chem.  Soc.’  1S82,  p.  351. 
t Ibid.  pp.  315,  351 . 
