340 
On  the  Power  of  Soils  to  absorb  Manure. 
monia,  which  would  be  added  to  the  quantity  absorbed  in  our  ex- 
periment. It  is  true  that  this  objection  extends  to  the  method 
adopted ; and  the  absorption  of  ammonia  in  the  instances  which 
follow  must  be  considered  to  represent  less  than  the  total  extent 
of  the  power,  since  many,  and  no  doubt  all  of  them,  are  already 
in  part  saturated  with  those  substances  with  which  they  have  a 
tendency  to  combine  ; but  it  is  plain  that,  supposing  the  direct 
examination  suitable  for  ammonia,  it  would  be  impossible  to 
adopt  it  for  potash,  magnesia,  &c.,  which  could  only  be  separated 
from  the  soil  that  had  absorbed  them  by  means  of  mineral  acids, 
which  would  at  the  same  time  dissolve  out  additional  quantities  of 
the  same  bases  existing  in  the  soil  as  ordinary  ingredients  of 
it.  Under  the  circumstances,  it  is  therefore  plain  that  the  dif- 
ferential method  was  the  only  one  available ; and  the  experi- 
ments that  follow  show  that  it  is  capable  of  very  considerable 
accuracy. 
In  operating  upon  ammonia  and  its  salts,  it  was  necessary,  in 
order  to  estimate  the  quantity  of  the  alkali  in  the  solution,  and  to 
separate  it  from  salts  of  lime,  &c.,  to  distill  the  resulting  liquid 
with  potash.  This  distillation  was  effected  in  a small  retort, 
having  attached  to  its  neck  a tube  with  a bulb  blown  upon  it. 
The  mouth  of  the  tube  dipped  into  hydrochloric  acid  in  a small 
bottle  immersed  in  cold  water,  but  all  possibility  of  the  liquid 
passing  back  into  the  retort  was  removed  by  the  bulb  on  the  tube. 
The  retort  was  furnished  with  a small  funnel,  by  which  the  ma- 
terials were  introduced.  In  order  to  ascertain  that  sufficient  pot- 
ash was  used,  a few  drops  of  an  infusion  of  sandal-wood  were 
added  to  the  liquid  in  the  retort. 
It  has  been  thought  necessary  to  describe  the  manner  in  which 
these  distillations  were  made,  because  it  is  usually  believed  that 
it  is  impossible  by  distillation  to  estimate  ammonia  with  very 
great  accuracy.  The  analyses,  however,  which  are  here  given, 
show  that,  with  proper  precautions,  the  method  gives  excellent 
results. 
The  acid  solution  of  sal-ammoniac,  produced  by  the  distillation, 
was  mixed  with  chloride  of  platinum,  evaporated  to  dryness, 
treated  with  alcohol  and  ether  in  the  usual  way,  and  the  resulting 
platinum  salt  dried  and  weighed. 
The  solution  of  ammonia  that  was  employed  for  the  experi- 
ments was  the  same  as  that  mentioned  before.  All  that  was  re- 
quired was  to  employ  a solution  of  manageable  strength,  and  to 
ascertain  exactly  what  that  strength  was.  Two  or  three  gallons 
of  ammoniacal  solution  were  made  by  mixing  the  strongest  solu- 
tion of  ammonia  with  from  fifty  to  sixty  times  its  weight  of  water. 
The  following  analyses  show  the  strength  of  this  solution  : — 
