328 
On  the  Power  of  Soils  to  absorb  Manure . 
Experiment  30. — White  clay  1000  grains,  sand  5000  grains,  forming  a 
filtering  column  of  18  inches;  ammoniacal  solution  of  ‘3  per  cent.  The 
solution  percolated  in  about  two  hours,  and  the  first  portions  of  liquid 
collected,  measuring  two  ounces,  were  decidedly  free  from  ammonia. 
Experiments  31  and  32. — Repetitions  of  the  preceding  experiments,  with 
similar  results. 
Experiment  33. — The  same  white  clay  strongly  heated  for  two  hours  in 
a covered  crucible.  When  used  as  a filter  it  did  not  require,  as  in  the 
previous  case,  to  be  made  pervious  by  admixture  of  sand.  A column  of 
18  inches  was  employed  with  solution  of  ammonia  of  ‘3  per  cent.  The 
first  half-ounce  which  passed  was  free  from  ammonia  or  its  salts,  but  the 
absorptive  power  appeared  sensibly  diminished,  though  anything  but 
destroyed. 
The  following  experiments,  illustrative  of  the  influence  of  acids 
upon  the  absorptive  powers  of  soils,  are  interesting : — 
Experiment  34. — Mr.  Huxtable’s  light  soil  was  digested  with  strong 
nitric  acid,  and  after  gentle  evaporation  to  dryness  the  mixture  was  ex- 
posed to  a heat  of  between  300°  and  400°  Fahr.  till  all  the  nitrous  fumes 
were  driven  off ; more  nitric  acid  was  then  added  and  heat  again  applied, 
the  operations  being  repeated  successively  till  the  nitric  acid  was  no  longer 
decomposed  upon  its  addition.  The  object  of  using  nitric  acid  was  to 
destroy  the  vegetable  matter  of  the  soil  without  the  necessity  of  heating  it 
to  such  an  extent  as  to  alter  the  chemical  arrangement  of  its  mineral 
ingredients.  The  prepared  soil  was  mixed  with  its  own  weight  of  sand,  a 
column  of  18  inches  of  the  mixture  being  employed,  and  standard  solution 
of  ammonia  passed  through  it.  The  liquid  when  it  came  through  was 
strongly  coloured  with  salts  of  iron,  and  gave  abundant  indications  of 
alumina,  as  might  be  expected:  but  nearly  two  ounces  passed  before 
ammonia  or  its  salts  could  be  detected  in  it. 
The  interest  of  this  experiment  consists  principally  in  the 
circumstance  that  the  destruction  of  the  vegetable  matter  does  not 
deprive  the  soil  of  its  power  of  absorbing  ammonia,  provided  that 
it  is  effected  by  agencies  which  do  not  materially  alter  the  mineral 
matters.  It  is  also  worthy  of  remark  that  the  conversion  of  any 
free  alumina  in  the  soil  into  a salt  of  that  base  does  not  destroy 
the  absorptive  power.  The  following  experiment  on  the  action 
of  hydrochloric  acid  is  still  more  important  in  the  latter  sense  : — 
Experiment  35. — The  same  soil  (Mr.  Huxtable’s)  digested  with  hydro- 
chloric acid  diluted  with  an  equal  weight  of  water.  The  materials  w’ere 
heated  nearly  to  boiling  for  several  hours,  and  were  then  left  to  digest  for  24 
hours,  being  frequently  shaken  during  that  time.  The  acid  liquid,  which 
contained  much  alumina  and  oxide  of  iron,  was  poured  off,  and  the  soil 
repeatedly  washed  with  distilled  water  till  all  traces  of  the  acid  were  re- 
moved ; it  was  then  carefully  dried.  The  soil  thus  prepared  was  mixed 
with  its  own  weight  of  sand,  and  upon  a column  of  the  mixture,  of  18 
inches  deep,  the  standard  solution  of  ammonia  was  poured.  The  liquid  took 
a long  time  to  filter,  but  when  it  came  through  neither  ammonia  nor  its 
salts  could  be  detected.  About  two  ounces  of  the  solution  had  passed 
before  any  ammoniacal  compounds  were  discovered  in  the  filtered  liquid. 
It  is  well  known  that  alumina  forms  a large  proportion  of  all 
fertile  soils,  and  it  is  not  at  all  certain  that  it  does  not  exist  in 
