332 
Nitrogen  as  Nitric  Acid , in  the  Soils 
the  surface.  Of  the  amount  of  nitrates  or  chlorides  which  may 
be  present  in  the  lower  depths  of  the  subsoil,  under  various 
circumstances,  we  have  as  yet  but  little  information.  In  the 
present  paper  attention  will  be  confined  to  the  amounts  of 
nitrates  found  in  the  soils. 
Method  of  Soil-sampling,  and  of  Analysis. 
The  samples  of  soils  have,  with  few  exceptions,  been  taken 
in  the  manner  first  adopted  at  Rothamsted  in  1356,  and  uniformly 
employed  since,  though  not  hitherto  described  in  this  ‘Journal.’ 
A rectangular  tube,  made  of  stout  sheet  iron,  6 inches  square  and 
generally  9 inches  deep,  having  a strong  rim  outside  its  upper 
edge,  is  driven  into  the  soil  until  the  upper  edge  is  level  with 
the  surface  of  the  land.  The  contents  of  the  tube  are  carefully 
removed  without  disturbing  its  position,  and  constitute  the 
sample  of  the  first  9 inches  of  soil.  If  a sample  of  the  second 
9 inches  is  to  be  taken,  the  empty  iron  tube  is  covered  with  a 
lid,  and  the  soil  surrounding  it  cleared  away  down  to  the  level 
of  its  lower  edge ; the  tube  is  then  again  driven  into  the  soil, 
till  its  upper  edge  is  at  the  level  which  its  lower  edge  pre- 
viously occupied  ; the  contents  of  the  tube  are  now  a sample 
of  the  second  9 inches  of  the  soil.  By  proceeding  in  this  way 
samples  may  be  taken  to  any  desired  depth.  An  iron  tube  12 
inches  square  is  sometimes  used  for  taking  a sample  of  the  sur- 
face soil  when  this  is  covered  with  vegetation. 
By  this  method  of  sampling  the  soil  and  subsoil  are  obtained 
in  their  true  proportion.  The  samples  taken  also  represent 
a known  area  and  depth  of  soil ; the  results  of  their  analysis 
consequently  admit  of  comparison  with  each  other ; the  con- 
stituents found  can  also  be  reckoned  into  pounds  per  acre.  It 
is  much  to  be  desired  that  the  taking  of  soil-samples  with  the 
spade  should  be  entirely  discarded.  Samples  so  obtained 
represent  variable  depths  and  no  definite  area,  and  they  can 
only  by  accident  include  the  true  proportion  of  soil  and  subsoil ; 
the  results  of  their  analysis  are  consequently  of  little  value  for 
purposes  of  comparison  or  calculation. 
Both  surface-soil  and  subsoil  being  more  or  less  irregular, 
it  is  always  necessary  to  take  samples  from  several  places  in 
the  same  plot  or  field.  The  samples  of  the  surface-soil  are, 
as  a rule,  kept  separate,  a mixed  sample  being  made  of  a part 
only,  and  the  remainder  reserved  for  reference  or  separate 
analysis.  The  samples  of  subsoil  are  generally  at  once  mixed. 
Each  sample  is  weighed  in  the  field  as  soon  as  collected  ; it  is 
then  broken  into  small  pieces,  spread  on  trays,  and  dried  in  a 
stove-room  at  a temperature  of  about  55°  C.  (131°  F.).  The 
