330 
On  the  Power  of  Soils  to  absorb  Manure. 
copious  ammoniacal  vapours  when  treated  with  potash.  Altogether 
three  ounces  of  the  liquid  percolated  without  a trace  of  ammoniacal 
salt,  but,  as  in  the  last  experiment,  sulphuric  acid  was  present  in  the 
very  first  portions,  combined,  as  in  the  previous  case,  with  lime.  So 
strongly  was  the  liquid  impregnated  with  sulphate  of  lime,  that  the  salt 
separated  from  it  in  flakes  after  standing  a few  minutes. 
In  the  two  experiments  just  described  we  meet  with  a remark- 
able circumstance.  Sulphate  of  ammonia  obeys  the  law  of 
absorption  so  far  as  the  ammonia  is  concerned,  but  its  acid  unites 
with  lime,  and  comes  through  in  solution.  The  salt  is  not 
absorbed  as  a whole,  but  only  the  base.  The  acid  with  which  it 
is  combined  forms  a soluble  salt  with  lime,  which  is  subject  to 
the  ordinary  laws  of  filtration,  and  is  not,  as  will  be  seen  pre- 
sently, in  any  way  retained  by  the  soil. 
The  power  of  absorption,  to  whatever  it  may  be  due,  would 
thus  seem  to  be  one  acting  only  on  the  alkaline  base,  and  not  on 
the  whole  salt.  And  in  this  respect  it  differs  entirely  from  a 
surface  attraction,  which  would  be  supposed  to  act  upon  the 
whole  salt.  The  fact  that  by  the  help  of  lime  the  soil  possesses 
the  same  power  for  the  retention  of  the  salts  of  ammonia  as  for 
the  free  base  itself,  opens  up  a mine  of  speculation  of  the  greatest 
promise  in  reference  to  practical  agriculture.  These  questions 
immediately  present  themselves  : — In  what  form  must  lime  exist 
in  the  soil  in  order  to  play  this  part  efficiently  ? Is  it  carbonate 
of  lime,  or  caustic  lime,  or  what  other  compound  of  this  base  ? Do 
all  soils  contain  sufficient  of  it  for  the  purpose?  and  if  not,  how 
will  it  be  best  applied  ? 
Reserving,  however,  such  inquiries  as  these  until  the  subject  is 
somewhat  more  fully  developed,  we  pass  on  to  give  an  account  of 
experiments  with  other  ammoniacal  salts. 
Nitrate  of  ammonia : — 
Experiment  40. — Mr.  Huxtable's  soil  mixed  with  its  own  weight  of  sand, 
the  filtering-bed  being  12  inches  in  depth.  The  solution  of  nitrate  of 
ammonia  employed  was  sufficiently  strong  to  give,  when  mixed  with 
potash,  abundance  of  ammoniacal  vapour.  The  first  portions  passed  in 
about  an  hour,  and  were  found  to  contain  no  portion  of  ammoniacal  salt. 
When  tested  by  sulphate  of  iron  and  sulphuric  acid  the  liquid  gave  abun- 
dant indications  of  the  presence  of  nitric  acid,  combined,  as  it  proved  upon 
examination,  with  lime. 
Experiment  41. — Nitrate  of  ammonia  in  solution  was  poured  upon  Mr. 
Pusey’s  soil— the  filter-bed  being,  as  in  the  last  case,  12  inches  deep.  A 
considerable  quantity  passed  through  without  any  ammoniacal  compound, 
but  affording  nitric  acid  from  the  first. 
Although  these  experiments  were  not  considered  in  the  light 
of  quantitative  trials  to  decide  the  extent  of  the  absorptive  power 
in  soils,  still  it  could  hardly  escape  notice  that  the  action  in  some 
cases  was  much  more  powerful  than  in  others.  In  the  last 
