336 
On  the  Power  of  Soils  to  absorb  Manure. 
Absorption  of  Carbonate  of  Lime. 
Experiment  55. — Carbonate  of  lime  (chalk)  was  diffused  through  water, 
and  a stream  of  carbonic  acid  gas  passed  into  the  liquid  for  some  time  ; the 
solution  wras  filtered  through  paper  to  clear  it  from  the  undissolved  chalk, 
and  was  then  passed  through  12  inches  of  Mr.  Pusey’s  soil.  The  filtered 
liquid  was  quite  free  from  lime  or  carbonic  acid. 
Experiment  56. — A specimen  of  water  from  a limestone  district  contain- 
ing upwards  of  80  grains  of  salts  of  lime  in  the  gallon  (three-fourths  of  this 
quantity  consisting  of  carbonate  and  the  other  of  muriate  and  sulphate), 
was  filtered  through  the  same  soil.  The  filtered  liquid  contained  sulphate 
and  muriate  of  lime  in  apparently  undiminished  quantity,  but  did  not 
afford,  upon  evaporation,  any  appreciable  quantity  of  carbonate. 
Experiment  57. — A similar  experiment  with  Thames  water,  the  filtering 
medium  being  a mixture  of  white  pottery  clay  and  fine  sand.  Several 
gallons  of  water  were  filtered  in  this  case  through  a filter-bed  of  about 
4 lbs.  of  the  above  materials.  With  the  exception  of  a little  sulphate  and 
muriate  of  lime,  which  salts  are  not  amenable  to  the  powers  of  the 
clay,  the  filtered  water  was  free  from  lime  ; it  did  not  contain  a trace 
of  carbonate.  (For  further  experiments  on  carbonate  of  lime,  see  p.  362.) 
These  experiments,  and  they  have  been  proved  to  be  correct 
by  frequent  repetition,  quite  establish  the  fact  that  lime  and  its 
carbonate  are  liable  to  detention  by  soils  with  which  these  solu- 
tions come  in  contact.  I have  no  doubt  that  the  history  of  the 
absorption  of  carbonate  as  well  as  of  caustic  lime  will  prove 
totally  different  from,  although  intimately  connected  with,  that  of 
the  other  substances  in  question.  But  our  attention  is  at  present 
confined  principally  to  the  facts,  and  the  explanation  of  those 
facts  must  in  great  part,  at  least,  be  reserved  for  further  com- 
munications. 
Absorption  of  Magnesia. 
The  base  magnesia  itself  cannot  form  the  subject  of  experi- 
ments in  filtration,  because  it  is  insoluble,  or  nearly  so,  in  wafer. 
The  carbonate  of  magnesia  is,  like  carbonate  of  lime,  insoluble 
in  water,  but  soluble,  like  it,  in  water  containing  carbonic  acid. 
The  power  of  soils  in  arresting  carbonate  of  magnesia  has  not 
been  tried,  but  from  the  experiments  on  its  other  compounds 
now  to  be  described  there  is  no  doubt  that  it  would  be  the  same 
as  for  carbonate  of  lime. 
Experiment  58. — Sulphate  of  magnesia.  100  grains  of  sulphate  of 
magnesia  were  dissolved  in  10,000  grains  of  water  (nearly  1£  pint),  form- 
ing a solution  containing  therefore  1 per  cent,  of  this  salt.  This  liquid 
was  passed  through  a filter-bed  of  10  inches  of  Mr.  Pusey’s  soil;  it  per- 
colated quickly,  and  gave,  when! tested,  abundance  of  sulphate  of  lime. 
The  lime,  being  precipitated  by  oxalate  of  ammonia,  the  solution  was 
examined  for  magnesia,  but  it  contained  none. 
Experiments  50  and  60.— Similar  experiments  with  muriate  and  nitrate 
of  magnesia,  affording  analogous  results ; the  acids  being  in  each  case 
found  in  the  filtered  liquid  in  combination  with  lime. 
