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On  the  Power  of  Soils  to  absorb  Manure. 
matters  and  salts — by  filtration  through  clay ; but  the  action 
appears  to  be  much  more  limited  than  when  the  urine  is  used 
in  a state  of  putridity.  Still  there  is  good  reason  to  hope  that 
in  the  case  of  fresh  urine  the  power  of  good  soils  is  practically 
sufficient.  Many  experiments  have  been  made  with  a view  of 
gaining  a general  notion  of  the  extent  of  the  power  in  question  ; 
in  one  instance  500  grains  of  clay  mixed  with  half  a pint  (J3500 
grains)  of  fresh  urine  deprived  it  of  colour,  and  carried  down  all 
the  animal  matter. 
Clay  appears  to  have  a remarkable  action  in  reference  to  the 
fermentation  of  organic  matters.  It  seems  indeed  to  oppose  fer- 
mentation, as  will  be  seen  in  the  following  experiment : — 
Experiment  94. — Three  quantities  of  fresh  urine,  of  2000  grains  each, 
were  measured  out  into  similar  glasses.  With  one  portion,  its  own  weight 
of  white  sand  was  mixed  : with  another,  its  own  weight  of  white  clay : the 
third  being  left  without  admixture  of  any  kind. 
When  smelt  immediately  after  mixture,  the  sand  appeared  to  have  had 
no  effect,  whilst  the  clay  mixture  had  entirely  lost  the  smell  of  urine:  they 
were  all  decidedly  acid  to  test  paper.  The  three  glasses  were  covered 
lightly  with  paper  and  placed  in  a warm  place,  being  examined  from  time 
to  time.  In  a few  hours  it  was  found  that  the  urine  containing  sand  had 
become  slightly  putrid  ; then  followed  the  natural  urine  ; but  the  quantity 
with  which  clay  had  been  mixed  did  not  become  putrid  at  all,  and  at  the 
end  of  7 or  8 weeks  it  had  only  the  peculiar  smell  of  fresh  urine,  without 
the  smallest  putridity.  The  surface  of  the  clay,  however,  became  after- 
wards covered  with  a luxuriant  growth  of  confervae,  which  did  not  happen 
in  either  of  the  other  glasses. 
This  is  a remarkable  experiment,  and  one  from  which  even- 
tually much  instruction  may  be  derived.  The  reason  that  the 
sand  accelerates  the  fermentation  of  the  urine  is  no  doubt  this  : 
all  bodies  possess  a surface  attraction  for  gases,  and  of  course 
therefore  for  common  air.  This  attraction,  which  enables  them 
to  condense  a certain  quantity  of  air  on  their  surfaces,  is  in  direct 
relation  to  the  extent  of  those  surfaces.  In  mixing  sand  with  the 
urine,  we  are  in  effect  exposing  the  latter  to  a largely  increased 
surface  of  air,  the  oxygen  of  which  is  necessary  to  commence  the 
putrefaction- — and  thus  hastening  the  changes  which  soon  or 
late  would  occur  in  the  urine  naturally.  But  what  shall  we  say 
of  the  action  of  the  clay?  that  it  retards  or  changes  the  nature  of 
the  putrefaction  is  evident ; but  the  question  is,  does  it  prevent 
the  conversion  of  the  animal  matters  into  the  ordinary  products  of 
decay ; or  does  it  allow  of  that  conversion  and  absorb  those 
products  as  they  are  formed?  This  is  a most  vital  question  to 
practical  agriculture,  clearly  affecting  our  views  of  the  state  in 
which  animal  manures  should  be  employed,  and  affecting  also  in 
the  highest  degree  the  theoretical  notions  of  vegetable  nutrition. 
Should  it  be  proved  that  the  clay  in  soils  possesses  the  power  of 
altogether  arresting  putrefaction,  and  that  urea  and  other  animal 
matters  remain  unchanged  in  the  soil,  we  shall  be  driven  to  allow 
