Vegetable  Chemistry. 
385 
riority  of  dung  for  turnips  be  due  to  its  nitrogen  or  to  its  carbon. 
For  wheat  it  was  due  to  nitrogen  (ammonia).  For  turnips,  Mr. 
Lawes  proves  it  to  be  due  to  carbon,  the  matter  of  wood.  In 
the  third  year  the  unmanured  portion  was  cross-dressed,  as 
follows : — 
Average  Weight  of  Roots. 
3 cwt. 
No  Cross-  lOcwt.  Sul]>li. 
Dressing.  Rapecake.  Ammonia.  Ammonia. 
No  manure  (third  season)  . . *11  ‘07  -07  -50 
Both  rape-cake  and  ammonia  are  nitrogenous,  but  rape-cake 
contains  carbon  besides.  Ammonia  single  does  harm  ; while  rape- 
cake,  as  in  other  cases,  has  been  beneficial.  Not  even  rape-cake,  in- 
deed, in  dry  weather  is  a safe  neighbour  for  turnips.  But  carbon 
appears  to  be  the  distinctive  active  principle  of  dung  for  turnips. 
Here  again  our  practice  is  borne  out  for  the  south  of  England. 
The  dung  is  applied  to  the  previous  crop  of  wheat,  which  gets, 
what  it  wants,  the  ammonia,  and  leaves  behind  what  it  does  not 
want,  the  woody  fibre  of  straw  (carbon),  for  the  turnip-crop, 
wdiich  receiving  also  bones  or  superphosphate,  is  satisfied.  Bran 
drilled  in  with  turnips,  containing  phosphorus,  acts  like  bones,  as 
does  also  guano.  The  upshot  of  the  whole  is  that,  practically,  so 
far  as  artificial  manures  are  concerned,  we  need  not  dwell  upon 
mineral  ingredients,  but  must  give  ammonia  to  wheat,  and  to 
turnips  phosphorus.  Under  what  circumstances  of  soil  or  weather 
ammonia  even  injures  turnips  remains  for  further  inquiry;  for 
good  farmers  give  them  guano,  rape-cake — nay,  near  Manchester, 
sulphate  of  ammonia  itself ; and  a neighbour'15  of  mine  has  raised 
fine  turnips  with  sugar-dross,  in  wdiich  the  blood,  that  is,  nitrogen 
must  be  the  active  principle : so  does  also  the  important  question, 
in  what  degree  carbon  (the  straw  of  our  dung)  is  beneficial  to 
them.  Though  the  mineral  theory  has  passed  away,  it  has  left  be- 
hind an  indifference  to  carbon.  Liebig,  however,  admits  that  woody 
matter,  decomposing  under  a seed,  feeds  it  until  it  can  derive 
its  carbon  from  the  atmosphere.  Boussingault  extends  this  action 
to  all  the  stages  of  growth.  I am  inclined  to  suspect  that  carbon, 
even  in  small  quantities,  is  a much  more  active  principle  than 
we  suppose.  There  is  the  case  of  bituminous  clay  improving  a 
grass  field  in  Wiltshire. f In  Trinidad,  decomposing  mineral 
bitumen  is  said  by  Lord  Dundonald  to  have  a strong  manuring 
effect.  These  act  probably  by  their  carbon  ; as  also  must  oil, 
* Mr.  Goodlake,  of  Wadley,  has  for  two  years  tried  this  manure,  at  the  rate  of 
I/.  3s.  6 d.  per  acre,  against  twenty  loads  of  dung.  The  rows  being  intermixed,  and 
the  crop  quite  level,  it  was  only  by  pulling  up  the  swedes  we  could  ascertain  how  each 
row  was  manured. 
f See  Mr.  Gowen-6  account  of  it,  Journal,  iv.  276. 
