Some  Secondary  Actions  of  Manures  upon  the  Soil.  27 
I 
being  burnt  off  is  not  found  in  the  ash.  Yet  in  this  connec- 
tion it  must  be  counted  as  an  acid  because  it  entered  the  plant 
as  nitrate  of  lime  or  soda — one  of  the  neutral  salts  originally 
present  in  the  soil  which  pass  into  solution  in  the  soil  water 
and  then  diffuse  through  into  the  plant’s  roots.  If  then  the 
nitrogen  is  calculated  as  nitric  acid  and  added  to  the  acids  in 
the  plant,  it  is  evident  that  the  ordinary  crop  must  have  taken 
from  the  soil  a greater  amount  of  the  acids  than  of  the  bases 
contained  in  the  salts  presented  to  it  as  food.  Table  V.  show 
this  relation  for  four  different  crops  at  Rothamsted,  the  figures 
given  for  acids  and  bases  being  equivalents,  i.e.,  reductions  to  a 
common  measure  in  which  one  of  any  acid  will  combine  with 
one  of  any  alkali,  while  in  the  last  two  lines  the  excess  of  base 
left  in  the  soil  is  recalculated  as  lb.  per  acre  of  carbonate  of 
soda  and  carbonate  of  lime  respectively  (see  Hall  and  Miller, 
Proc.  Roy.  Soc.,  1905,  B.  77,  1). 
Table  V. — Acids  and  Bases  in  Crops  reduced  to  Equivalents. 
Wheat 
Barley 
Swedes 
Hay 
Bases : 
Ferric  oxide 
003 
004 
009 
017 
Lime  ....... 
0-36 
0-46 
1-24 
103 
Magnesia  ...... 
0-33 
0-34 
0-35 
0-60 
Potash  ...... 
0-78 
0-68 
1-99 
2-64 
Soda  ....... 
003 
009 
0-36 
0-44 
Total  ..... 
1-53 
1-61 
4-03 
4-86 
Acids : 
Phosphoric  ...... 
0-87 
0-90 
102 
118 
Sulphuric  ...... 
0-14 
0-15 
0-80 
0-50 
Chlorine  ...... 
0-09 
015 
0-30 
1-47 
Nitrogen 
300 
2'97 
6-74 
5'35 
Total 
410 
4-17 
8-86 
8-50 
Excess  of  acid  ..... 
2-57 
2-56 
4-83 
3-62 
Equivalent  to  carbonate  of  lime  . 
129 
128 
242 
181 
Equivalent  to  carbonate  of  soda  . 
136 
135 
256 
192 
From  these  results  it  is  apparent  that  if  the  plant  contains 
such  an  excess  of  acid  it  must  leave  behind  in  the  soil  a corre- 
sponding excess  of  base,  because  the  food  salts  in  the  soil  are  in 
the  main  neutral  compounds.  At  this  rate  the  plant  ought  to 
make  a medium  in  which  it  is  growing  progressively  more 
basic,  or  alkaline  if  the  bases  set  free  happen  to  be  soluble  ; 
and  some  of  the  earlier  observers  like  Knop  and  Stohmann 
