On  the  Power  of  Soils  to  absorb  Manure. 
335 
of  caustic  lime  should  not  be  arrested  in  the  same  way  as  caustic 
potash  or  ammonia  is,  for  in  these  cases  the  action  seems  to 
be  simple  and  direct.  Accordingly  we  find  that  lime-water  is 
entirely  deprived  of  its  lime  by  fdtration  through  a soil,  as  shown 
by  the  following  experiment : — 
Experiment  51. — Lime-water  of  moderate  strength  was  poured  upon  a 
mixture  of  white  pottery  clay  with  sand,  forming  a filter  of  12  inches  in 
depth.  A considerable  quantity  of  liquid  passed  without  bringing  through 
any  portion  of  lime,  either  free  or  in  combination. 
Experiments  52,  53,  and  54. — Similar  experiments  with  lime-water  and 
three  different  subsoil  clays  of  the  gault  formation,  obtained  from  Mr. 
Paine’s  land  at  Farnham.  In  all  these  cases  a large  quantity  of  lime  was 
arrested. 
For  further  illustrations  of  the  power  of  soils  to  arrest  free  lime,  see 
page  3C1. 
Obviously,  then,  lime  in  the  free  state,  uncombined,  that  is, 
with  any  acid,  is  detained  by  soils  in  much  the  same  way  .as  the 
other  bases.  I have  reason,  however,  to  think  that  the  power  to 
arrest  lime  is  in  quantity,  at  least,  not  at  all  in  relation  to  the 
power  to  arrest  other  bases,  and  that  indeed  the  combination  with 
lime  is  a proof  that  the  soil  is  not  in  the  best  condition  for  the 
detention  of  other  alkaline  and  earthy  bases.  Leaving,  however, 
this  point  for  discussion  at  a much  more  advanced  stage  of  our 
investigation,  we  will  proceed  to  ascertain  whether  carbonate  of 
lime  is  at  all  subject  to  removal  from  solution  and  filtration 
through  soils.  It  has  been  seen,  indeed,  that  the  carbonates  of 
potash  and  ammonia  are  arrested  by  the  soil  apparently  as  a 
whole- — that  is  to  say,  neither  the  acid  nor  the  base  is  found  in 
the  filtered  liquid.  This  result  may  be  viewed  in  two  ways : 
either  that  the  absorptive  power  of  the  soil  exists  equally  for  the 
carbonates  and  the  caustic  alkali ; or,  that  the  base  being  ab- 
sorbed, the  carbonic  acid  is,  as  in  all  the  other  salts,  transferred 
to  lime,  and  the  carbonate  of  lime  so  formed  is  only  absent  from 
the  filtered  liquid  on  account  of  its  insolubility  in  water.  This 
second  mode  is  by  far  the  most  pi'obable,  and,  if  true,  would  de- 
cide the  question  against  carbonate  of  lime  in  the  soil  being  the 
means  of  transformation — for,  were  it  so,  the  filtration  of  carbonate 
of  ammonia  and  potash  through  a soil  should  afford  a corresponding 
quantity  of  bi-carbonate  of  lime  in  the  resulting  liquid,  which  is  not 
found  to  be  the  case.  But  the  stoppage  of  carbonates  of  potash 
and  ammonia  by  the  soil  does  not  necessitate  a similar  retention  of 
carbonate  of  lime,  seeing  that  the  latter  exists  when  in  solution  only 
as  the  bi-carbonate  of  lime,  that  is  to  say,  carbonate  of  lime  dis- 
solved by  an  extra  dose  of  carbonic  acid.  To  detain  the  car- 
bonate of  lime  the  soil  must  then  be  able  to  deprive  it  in  some 
way  of  its  extra  carbonic  acid.  That  soils  have  this  faculty,  the 
following  experiments  will  demonstrate. 
