384 
Vegetable  Chemistry. 
1. 
Superphosphate  G35lbs. 
Sulph.  Ammonia  . 
P.usli. 
65  lbs.  214 
2. 
V arious  salts 
. 619  „ 
Ditto 
65  ,, 
21* 
Ditto  . 
. 619  „ 
Rapecake  ( nitrogenous ), 
156  , , 
22f 
4. 
Ditto  . 
. 646  „ 
Sulph.  Ammonia  . 
80  ,, 
26* 
The  ammonia  at  once  raises  the  wheat  crop  from  16  bushels 
to  21,  that  is,  to  about  the  level  of  the  dung;  and  as  more 
ammonia  is  given,  more  wheat  is  grown  reaching  26  bushels, 
and  surpassing  what  the  dung  can  produce.  These  figures  are  con- 
clusive that  the  action  was  in  the  nitrogen  (ammonia)  of  the  dung, 
not  in  its  charcoal ; and  upon  these  experiments  rests  the  now  esta- 
blished doctrine  that  nitrogen  is  what  white  crops  require.  And  it 
may  generally  be  assumed  for  practical  purposes  that  if  ammonia 
be  supplied  to  wheat,  it  will  find  the  mineral  ingredients  for  itself, 
either  in  the  soil  or  in  past  or  present  dressings ; not  that  pure 
ammonia  can  be  supplied,  for  pure  ammonia  is  too  dear — but  all 
the  manures  practically  applied  by  farmers  to  wheat  hitherto  are 
of  a nitrogenous  ( ammoniacal ) character,  namely: — 
Dung.  Rape-cake.  Guano-. 
Sheep-folding.  Shoddy.  Nitrate  of  soda. 
Woollen  rags.  Sprats,  &c.  Seaweed. 
Thus  experience  is  borne  out  by  science. 
The  Rothamstead  experiments  on  turnips  are  far  more  com- 
plicated, but  I will  endeavour  to  make  a fair  selection.  They  were 
equally  tried  on  exhausted  land,  and  repeated  on  the  same  ground 
for  three  years,  the  turnips  being  drawn  from  the  land.  The 
produce  per  acre  is  as  follows  : — 
Season. 
1843  . 
1844  . 
1845  . 
No  Manure. 
Dung 
12  tons. 
Superphosphate 
of  Lime. 
Mixed  Farthy  and 
Alkaline  Phosphates. 
Tons. 
cwt. 
Tons.  cwt. 
Tons.  cwt. 
Tons.  cwt. 
4 
3 
9 
9 
12 
3 
11 
17 
2 
4 
10 
15 
7 14 
5 
13 
0 
13 
17 
0 
12 
13 
12 
12 
Here  we  find  a result  very  different  from  the  former  one.  The 
simple  phosphorus  which  did  nothing  for  wheat  nearly  equals  the 
dung  for  turnips.  Rut  the  mineral  theory  equally  fails.  For  while 
20  tons  of  turnips  contain  45  lbs.  of  phosphorus,  they  contain  173 
lbs.  of  alkalies,  potash,  and  soda — so  much  indeed  that  they  were 
classed  in  the  alkaline  family  as  specially  requiring  to  be  manured 
with  alkalies  ; yet  not  only  is  the  average  crop  produced  by  alkaline 
salts  ( column  4)  the  worst  of  the  three — but  the  application  of 
potash  diminished  the  size  of  the  bulbs,  and  Mr.  Lawes  observed 
that  “ by  the  direct  supply  of  alkalies  no  good  effect  has  arisen  in 
the  season  of  application  ; that  they  are  rarely  if  ever  requisite  ; 
and  if  ever,  should  not  be  applied  in  their  alkaline  condition.” 
Superphosphate,  however,  is  slightly  inferior  to  dung,  and  the 
question  again  arises  as  under  wheat,  whether  this  slight  supe- 
