On  the  Power  of  Soils  to  absorb  Manure. 
317 
bases,  for  so  far  as  the  experiments  have  gone  they  appear  to  be 
wholly  insoluble  in  pure  water.* 
There  is  a further  power  possessed  by  sand  in  relation  to 
organic  solutions  which  it  is  very  necessary  to  advert  to  in  order 
that  it  may  not  be  taken  in  explanation  of  the  faculty  which  soils 
will  be  shown  to  possess  of  arresting  organic  and  especially 
animal  matters.  Dr.  Angus  Smith,  in  his  examination  of  the 
waters  of  towns,  had  frequently  observed  the  presence  of  large 
quantities  of  alkaline  nitrates  in  the  water  of  shallow  wells. 
Suspecting  the  animal  origin  of  this  nitric  acid,  he  instituted  ex- 
periments upon  the  action  of  filters  of  sand  and  other  porous 
bodies  upon  solutions  of  different  animal  and  vegetable  matters, 
and  he  found  that  in  such  circumstances  oxidation  took  place 
most  rapidly — the  nitrogen  of  organic  matters  being  converted 
into  nitric  acid,  the  carbon  and  hydrogen  also  combining  with 
oxygen  at  the  same  time.  Thus  a solution  of  yeast,  which  con- 
tained no  nitric  acid,  after  being  passed  through  a filter  of  sand 
gave  abundant  evidence  of  salts  of  this  acid.  Coloured  solutions 
were  in  this  way  more  or  less  decolorized.  Water  rendered 
brown  by  peaty  matter  was  found  to  be  purified  by  filtration 
through  sand.  These  and  other  very  interesting  experiments  are 
explained  by  Dr.  Smith  on  the  principle  that  sand  by  its  surface 
attraction  for  air  is  a powerfnl  oxidating  agent,  and  that  the 
filtration  through  such  a medium  is  the  most  perfect  way  of  ex- 
posing a solution  to  the  influence  of  oxygen. 
Dr.  Smith’s  experiments  serve  to  explain  the  rapidity  with 
which  manure  disappears  from  sandy  soils,  but  it  is  clear  that 
there  is  a power  of  an  opposite  kind  brought  into  action  in  good 
loamy  soils  which  retain  manure,  although  in  extent  of  acting 
surface  and  permeability  to  the  air,  they  are  little  if  at  all  in- 
ferior to  sandy  land.  This  power  is  evidently  that  of  clay,  which 
will  be  seen  as  we  proceed  to  be  antagonistic  to  the  oxidating 
power  of  sand,  combining  with  organic  matters,  and  retarding 
rather  than  hastening  their  destruction.  Nitric  acid  has  not  in 
any  case  been  found  in  these  experiments  to  be  a product  of  the 
filtration  of  organic  matters  through  soils  containing  a fair  share 
of  clay,  whilst,  on  the  other  hand,  colouring  matters  are  actually 
* Mr.  Beniays,  in  a communication  to  the  Agricultural  Gazette  (Oct.  20th,  1S-J9), 
describes  some  simple  experiments  of  filtration  made  by  him,  the  result  of  which 
is  evidently  due,  partly  to  the  law  of  capillarity,  and  partly  to  the  chemical  action  of 
the  soil.  Mr.  Bernays  found  that  a solution  of  common  salt  was  diminished  in 
strength  by  filtratiou  through  a soil,  and  that,  the  diminution  was  in  proportion  to  the 
depth  of  the  filtering  column,  and  he  used  this  as  an  argument  for  deep  drainage. 
The  depth  of  the  filtering  column  has  no  further  influence  upon  the  result  than  that 
it  brings  into  play  a larger  quantity  of  the  absorbent  substance ; and  since  different 
soils  are  shown  in  the  present  paper  to  possess  a different  power  of  absorption,  no  absolute 
rule  for  the  depth  of  drainage  can  be  founded  on  this  property  of  soils. 
