On  the  Power  of  Soils  to  absorb  Manure. 
371 
whole — of  those  ingredients  of  manure  upon  which  we  are  accus- 
tomed to  place  the  most  value.  And  to  what  extent  does  this 
action  take  place?  The  absorption  extends  to  a weight  of  sew- 
age-water more  than  equal  to  the  weight  of  the  soil,  and  how  much 
further  it  might  have  gone  we  know  not,  because  the  experiment 
was  not  carried  beyond.  If  in  practice  every  portion  of  the  soil 
of  an  acre  of  land  could  have  been  brought  into  activity  as  a filter 
for  this  sewer-water,  and  that  the  soil  so  saturated  had  been  but 
10  inches  deep,  1000  tons  or  224,000  gallons  of  undiluted 
sewage-water  might  be  thrown  upon  it,  and  the  water  would  have 
passed  away  by  the  drains  deprived  of  its  principal  manuring 
properties. 
Now  1000  tons  or  224,000  gallons  of  this  sewer-water  would 
contain,  according  to  the  analysis,  about  half  a ton  of  real 
ammonia,  and  other  things  in  proportion.  In  other  words,  to 
put  on  a quantity  of  this  sewage  equal  to  the  weight  of  the  soil 
to  the  depth  of  10  inches  would  be  to  manure  an  acre  of  land  with 
3 tons  of  Peruvian  guano,  which  is  fully  20  times  the  quantity 
that  would  actually  be  employed. 
I would  carefully  guard  my  readers  from  supposing  that  this 
argument  is  meant  to  apply  literally  to  practice.  It  is  of  course 
impossible  to  render  the  soil  of  a field  so  equally  permeable  as 
that  used  in  the  small  experiment  just  described,  but  with  the 
caution  that  such  is  the  result  under  the  most  favourable  condi- 
tions, it  can  do  no  harm,  but  much  good,  to  bring  forward  a cal- 
culation which  shows  that  a good  and  well  comminuted  soil, 
sufficiently  porous  to  allow  of  the  gentle  descent  of  liquids,  and 
yet  not  so  open  or  fissured  as  that  they  should  find  their  way  by 
what  may  be  called  perpendicular  drains  into  the  ordinary  drains 
below,  and  above  all,  containing  a fair  amount  of  the  absorbing 
ingredient,  the  clay, — that  such  a soil  will  receive  and  retain  many 
times  the  quantity  of  manure  that  is  likely  to  be  put  upon  it  in  the 
ordinary  course  of  management,  without  the  smallest  need  for 
fear  on  the  part  of  the  farmer  that  it  shall  be  lost  in  the  drains,' 
provided  that  the  preservative  powers  of  the  soil  be  properly  un- 
derstood and  brought  into  play, 
I shall  forbear  in  the  present  paper  from  giving  any  very  pre- 
cise opinion  as  to  the  cause  of  the  absorbent  power  which  we 
have  been  studying.  Those  who  have  taken  the  trouble  to  read 
the  account  of  the  experiments  will  have  seen  that  they  dispose 
of  some  of  the  forms  of  explanation  which  might  have  been  sug- 
gested, and  at  the  same  time  reduce  the  question  to  a much 
narrower  compass ; but  it  would  be  premature  to  offer  an  opinion 
which  it  is  hoped  will  be  much  more  worthy  of  consideration 
when  the  inquiry  shall  have  been  further  prosecuted.  It  is  right, 
however,  to  mention  here  that  silica,  in  the  state  in  which  it  mav 
2 B 2 
