74 
On  the  Absorbent  Power  of  Soils. 
soil  whilst  still  hot,  and  10  grs.  sulph.  and  sesquicarb.  amm. 
dissolved  in  10  drains  of  water,  poured  over  the  surface  of  A and 
B respectively.  Eight  oz.  of  boiled  distilled  water  (cold)  were 
immediately  added  to  each.  The  soil  being  dry,  retained  a 
large  portion  of  the  water,  but  oz.  were  obtained  to  operate 
on,  and  the  following  result  obtained  by  the  process  before  de- 
scribed : — 
A gave 
B gave 
Grains. 
1 '2  sulphate  of  lime. 
• 1 sulphate  of  ammonia. 
Trace  of  ammonia  and 
organic  matter. 
If  this  be  compared  with  Experiment  1,  where  water  was,  as 
in  this  instance,  passed  once  only  through  the  same  description 
of  soil,  it  will  be  seen  that  after  the  drying  process,  which  bore 
a considerable  resemblance  to  the  ordinary  agricultural  operation 
of  fallowing,  the  soil  seemed  to  have  acquired  a still  greater 
power  of  retaining  ammonia  than  before.  The  mode  in  which  it 
was  effected,  however,  had  no  additional  light  thrown  upon  it. 
The  next  experiment  I tried,  and  the  last  that  I shall  mention 
on  this  occasion,  was  one  to  ascertain  whether  the  affinity  of  the 
soil  for  salts  of  ammonia  extended  to  other  salts.  Ten  grains  of 
common  salt  were  mixed  with  a portion  of  the  soil  last  mentioned, 
and  water  poured  upon  it  till  12  oz.  had  passed  through ; on 
evaporation  9 grains  of  salt  were  indicated  by  its  equivalent  of 
chloride  of  silver  being  obtained.  Nine-tenths  of  the  salt  applied 
were  thus  washed  out  unchanged  by  the  first  12  oz.  of  water 
which  passed  through  the  soil  ; and  the  inference  is  clear,  that  if 
the  application  of  common  salt  be  of  any  service  to  light  land,  the 
benefit  can  only  be  of  a very  temporary  nature,  as  a few  rainy 
days  will  wash  it  all  out. 
This  set  of  experiments  is  very  imperfect,  but  it  suggests  many 
interesting  questions  which  I hope  to  have  leisure  to  follow  up 
ere  long,  and  in  the  mean  while  the  results  obtained  have  furnished 
me  with  useful  practical  hints,  and  may  perhaps  be  regarded 
with  some  interest  as  the  first  discovery  of  a highly  important 
property  of  soils,  the  knowledge  of  which  can  hardly  fad  to  be 
l)eneficial  to  agriculture. 
Yours,  very  truly, 
H.  S.  Thompson. 
Moat  Hall,  June , 1850. 
