248 
ON  NASCENT  MANURES. 
sary  to  remove  the  plastering,  in  order  to  get  rid  of  erisypelas 
and  other  diseases. 
Nearly,  or  quite  all  of  the  nitric  acid  of  commerce,  was  no 
doubt  originally  derived  from  ammonia  in  the  order  above  referred 
to,  for,  if  my  theory  as  above  stated  is  admitted,  then,  every  au- 
thority will  sustain  me  in  saying  that  old  plaster  contains  ammo- 
nia, and  this  ammonia  is  converted  into  nitric  acid  on  the  wall. 
Salts  of  nitric  acid  can  be  seen  by  any  one  on  the  surface  of 
old  walls.  Moreover,  the  leachings  of  old  walls  have  frequently 
been  used  in  the  manufacture  of  gunpowder,  and  old  plaster  al- 
ways enters  into  the  composition  of  artificial  nitre  beds. 
It  will  be  readily  admitted  that  silica  can  never  enter  the  root- 
let of  a  plant,  however  fine  the  powder,  unless  it  is  in  solution, 
and  that  the  finest  powder  of  sand  or  silica  differs, as  much  in  solu- 
bility from  nascent  silica,  as  sand  differs  from  sugar.  The 
importance,  then,  of  soluble  silica  to  grasses  and  wheat,  and 
especially  to  corn,  and,  indeed,  its  value  as  manure  has  long 
betn  recognized ;  (see  Liebig's  Chemistry,  Am.  Ed.  1841,  p. 
200.) 
It  was  first  supposed  that  potash  was  the  vehicle  for  its  convey- 
ance to  every  part  of  the  plant ;  but  the  modern  idea  is,  that  am- 
monia is  the  main  instrument  of  its  conveyance  ;  certain  it  is  that 
it  loses  its  base  at  the  instant  of  its  deposition  on  the  stem ;  and 
if  potash  were  the  base,  then  it  would  be  necessary  that  the  pot- 
ash be  carried  back  again  to  the  earth,  and  the  plant  would  be 
constantly  embarrassed  by  excrementitious  matter;  whereas,  the 
ammonia  being  volatile  evaporates,  and  leaves  the  glassy  coating, 
or  element  of  strength,  on  the  surface  of  the  stem.  Thus,  it  is 
found  that  more  ammonia  is  actually  exhaled  from  plants,  than  we 
ever  give  them  in  the  form  of  manure  ;  and  it  is  strongly  suspect- 
ed that  soluble  silica  is  really  the  manure,  while  ammonia  is 
merely  the  vehicle  for  the  conveyance  of  soluble  silica  through 
the  plant. 
When  the  carcass  of  an  animal  falls  in  a  field,  the  luxuriant 
grass  or  grain  "  falls,"  on  account  of  the  absence  of  the  relative 
amount  of  soluble  silica,  or  the  excess  of  ammonia  uses  up  at 
once  all  of  this  necessary  element  that  is  available. 
Two  years  since,  I  manured  two  lands  in  the  centre  of  my  oats 
field,  the  one  with  Peruvian  Guano,  the  other  with  soluble  silica, 
