338 
On  the  Power  of  Soils  to  absorb  Manure. 
with  the  bi-phosphate  would  convert  the  whole  of  the  phosphoric 
acid  into  an  insoluble  phosphate;  but  at  the  same  time  it  seems 
to  follow,  from  all  that  has  been  said,  that  a soil  containing  no 
portion  of  lime  in  the  form  of  carbonate,  would  perfectly  retain 
the  phosphoric  acid  of  superphosphate  of  lime. 
These  observations  have  preceded  the  account  of  the  actual 
experiments,  because,  with  a knowledge  of  the  actions  previously 
described,  the  results  are  only  such  as  would  with  tolerable  cer- 
tainty have  been  predicted. 
Absorption  of  Phosphoric  Acid  by  Soils. 
Experiment  61. — A filtering-jar  was  partially  filled  with  Mr.  Pusey's 
soil ; it  contained  perhaps  about  1 lb.  of  soil.  Through  this  soil  a solution 
of  phosphate  of  soda  was  passed.  About  10  oz.  of  the  filtered  liquid 
were  collected  and  tested  tor  phosphoric  acid  in  comparison  with  the 
original  solution.  The  latter  gave  abundance  of  pyrophosphate  of  mag- 
nesia, but  no  evidence  of  phosphoric  acid  could  be  obtained  in  the  filtered 
liquid. 
Experiment  62. — The  ash  of  Peruvian  guano  (which  is  principally 
phosphate  of  lime)  was  dissolved  in  dilute  sulphuric  acid,  an  excess  of  the 
phosphate  being  employed.  The  solution  was  made  clear  by  filtering 
through  paper  and  was  then  thrown  upon  a filter-bed  of  soil  similar  to 
that  employed  in  the  last  experiment.  When  8 ounces  of  liquid  had 
passed  the  solution  was  tested,  but  no  phosphoric  acid  could  be  detected 
in  it. 
These  experiments  are  quite  sufficient  to  prove  that  phosphoric 
acid,  though  not  subject  to  direct  absorption  by  any  ingredients 
of  the  soil,  is  yet  indirectly  retained  by  it. 
On  the  Extent  of  the  Power  of  Soils  to  absorb  Ammonia , Pot- 
ash, 8fc. — The  experiments  hitherto  recorded  speak  only  of  the 
fact  that  ammonia,  potash,  magnesia,  &c.,  are  absorbed  and  ren- 
dered insoluble  by  soils — affording,  however,  indications  of  this 
power  being  very  considerable,  and  in  all  probability  abundantly 
sufficient  for  the  preservation  of  the  various  salts  from  loss  by 
washing  of  the  soil.  It  seemed  very  important  also  to  ascertain 
to  what  extent  the  property  in  question  was  exhibited  in  soils — 
whether  it  was  the  same  for  all  soils — and  whether,  in  the  same 
soil,  it  was  equal  for  the  different  alkaline  bases.  To  obtain  a 
solution  of  these  questions  required  the  employment  of  rigorous 
quantitative  analysis  ; and  although  much  remains  to  be  done  even 
in  this  department  of  the  subject,  the  experiments  which  follow 
will,  it  is  hoped,  convey  a very  fair  general  notion  of  this  pro- 
perty of  soils.  In  entering  upon  this  portion  of  the  inquiry,  it 
was  soon  found  that  the  method  of  filtration,  although  extremely 
convenient  in  the  earlier  and  preliminary  experiments,  could  not 
be  satisfactorily  employed  in  determining  the  amount  of  absorptive 
power.  However  finely  and  uniformly  a soil  may  be  divided, 
