34  Some  Secondary  Actions  of  Manures  U2mn  the  Soil. 
' Deflocculation  brought  about  by  potash  salts  or  by  common 
salt  is  rarely  a matter  of  much  practical  importance,  but  it  may 
be  obviated  by  using  superphosphate  as  the  phosphatic  manure 
going  with  the  potash  salts,  and  again  by  applying  the  latter 
fertiliser  in  the  winter.  This  will  give  time  for  the  reactions 
between  fertiliser  and  soil  to  be  completed  and  for  some 
of  the  useless  bye-products  like  the  carbonate  of  soda  to  be 
washed  out.  If  on  arable  land  there  will  also  be  time  for  the 
spring  frosts  to  restore  the  texture  of  the  land  before  the 
preparation  of  the  seed  bed  is  taken  in  hand.'  No  fear  need  be 
entertained  that  the  valuable  potash  salts  will  be  washed  out 
of  the  soil.  "Way’s  and  Voelcker’s  papers  show  that  they  are 
retained,  and  Dr.  B.  Dyer,  in  his  examination  of  the  Rotham- 
sted  soils,  found  that  of  the  potash  annually  applied  and  not 
utilised  by  the  crop  very  little  had  been  washed  away,  even 
after  flfty  years  of  the  treatment. 
It  will  be  noticed  that  all  the  effects  of  fertilisers  upon  soil 
which  have  been  discussed  are  due  to  chemical  changes  of  a 
comparatively  minor  order  which  were  overlooked  or  not 
suspected  when  fertiliser  actions  first  began  to  be  studied, 
because  in  most  cases  the  agent  in  the  process  is  that  part  of 
the  substance  which  possesses  no  value  as  a fertiliser.  For 
example,  sulphate  of  ammonia  was  considered  as  a source  of 
nitrogen  only,  the  sulphuric  acid  it  contained  was  entirely 
ignored  and  regarded  as  of  no  account.  Similarly  with  nitrate 
of  soda  the  nitrogen  is  the  important  part  upon  which  its  value 
as  a fertiliser  depends  ; the  mistake  came  in  supposing  that 
the  soda  was  entirely  without  effect.  The  same  state  of  affairs 
has  occurred  over  and  over  again  in  the  history  of  science  ; 
the  broad  conclusions  reached  by  early  generations  of  in- 
vestigators, which  become  the  staple  of  the  text  books  and 
the  dogma  of  the  lecture  rooms,  and  in  the  process  always 
grow  cruder  and  more  hard  and  fast  in  statement  than  is 
justified  by  the  original  researches,  prove  eventually  to  be  no 
more  than  flrst  approximations  to  the  truth.  To  complete  the 
story,  a second,  sometimes  even  a third,  term  requires  to  be 
introduced,  the  course  of  events  in  nature  being  always  much 
more  complex  than  the  nice  watertight  statements  which  our 
minds  like  to  evolve  under  the  guise  of  laws.  These  second 
approximations,  which  may  become  large  enough  to  override 
the  main  truth,  often  make  themselves  evident  to  the  practical 
man,  who  delights  in  them  as  proofs  that  theory  and  practice 
do  not  always  square,  though  as  theory  can  never  be  more  than 
a method  of  explaining  and  in  its  turn  predicting  the  practice, 
any  want  of  agreement  between  the  two  must  only  mean  that 
the  practical  man  is  dealing  with  an  imperfect  theory. 
However  it  is  the  duty  of  the  scientific  man  to  recognise  that 
practical  affairs  will  always  be  stretching  the  range  of  actions 
