May  1,  1896.] 
Supplement  la  the  “ Tropical  Agriculturist:' 
801 
past  been  steadily  increasing.  That  it  is  being 
employed  by  the  cake-makers  in  the  fabrication  of 
what  is  known  in  the  trade  as  certain  tjiialities  of 
linseed  cake  there  would  seem  to  be  no  doubt. 
Castor-Cake. — In  India  this  is  one  of  the  most 
highly-valued  of  all  oil-cake.s  as  a manure.  In 
Europe  it  has  aci(uired  an  evil  repute  as  one  of  the 
most  dangerous  substances  when  used  in  the  fabri- 
cation of  inferior  qualities  of  liu.seed  cake.  In 
commerce  it  appears  to  be  sometimes  designated 
Jatropha  manure.  Morton  in  his  Cyclopoedia  of 
agriculi  ure  has  tlie  following  passage  : — ^This  cake 
can  only  be  used  as  a manure  ; for  feeding  pur- 
poses it  is  entirely  unsuited,  as  the  oil  still  remain- 
ing in  the  cake  is  exceedingly  purgative  and  poi- 
sonous. This  maiufe  was  recently  analysed  by 
Mr.  Thomas  Ilerapath  who  found  it  to  contain  in 
100  parts:  water  10'24  ; nitrogen  in  fresh  cake 
4'20  ; nitrogen  in  dry  cake  4 68  ; ash  7 ’88.  The 
ash  itself  contained  in  100  parts:  soluble  salts 
6T93  ; carbonates  21‘07  ; insol.  phosphates  53’554  ; 
silica  &c.  19T83. 
I’erhaps  a more  instructive  table  of  analysis  of 
castor  cake  is  that  published  by  the  late  Trof. 
Ander.son  of  Glasgow  in  his  Agrieultival  Chemis- 
try: Water  12  31  ; oil  24'32 ; albuminous  com- 
pounds 21'91  (containing  nitrogen  3 20) ; mucilage, 
sugar,  fibre  &c.  35'3S  ; ash  (5 ‘08.  The  ash  contained 
silica  equal  to  1'96,  pho.sphates  2 81,  and  phospho- 
ric acid  in  combination  with  alkalis  ’64. 
SOIL  ANALYSIS. 
By  F.  B.  Guthrie. 
{Continued.) 
By  the  porosity  of  a soil  is  meant  the  fineness 
and  numbet  of  its  pores.  We  must  distinguish 
between  this  and  permeability  to  water ; a coarse 
sand,  for  example,  being  permeable  to  water,  but 
possessing  properties  exactly  opposed  to  those  of  a 
porous  soil.  Humus  soils  are  esjrecially  porou.«. 
On  the.fineness  of  texture  depend  the  following 
characteristics - 
The  capillary  power,  by  which  is  understood  the 
power  of  imbibing  water.  This  property  main- 
tains a continual  circulation  of  water  witliin  the 
soil,  and  consequent  aeration.  It  is,  moreover, 
largely  through  the  agency  of  this  circulating 
water,  which  is  charged  with  carbonic  acid  and 
different  salts,  that  the  mineral,  and  in  a less 
degree  the  organic  matter,  of  the  soil  is  rendered 
available  for  plant  food  and  presented  in  solution 
to  the  plant. 
The  capillary  power  of  a soil  depends  very 
largely  upon  the  fineness  of  its  texture.  The 
nearer  the  texture  approaches  that  of  a sponge  the 
greater  will  be  its  capillarity. 
Humus  has  a very  high  capillary  power,  which 
is  not  possessed  to  any  extent  by  either  coarse  sand 
or  clay. 
This  property  is  determined  by  filling  a tube  of 
known  length  with  the  finely  powdered  air-dried 
soil ; the  tube  is  open  at  both  ends,  the  lower  end 
• being  closed  by  a piece  of  fine  muslin,  and  stands 
in  water.  At  the  end  of  twelve  or  twenty-four 
hours  Urn  height  to  which  the  water  has  visibly 
risen  in  the  tube  is  read  off.  The  determination 
presents  no  special  difficulty,  and  I will  not  waste 
your  time  with  long  descriptions  of  this  or  other 
methods  mentioned  here.  They  are  all  capable  of 
being  rapidly  and  accurately  performed, 
The  capacity  of  a soil  for  water  is  also  ot  special 
interest,  and  depends  partly  upon  its  porosity  and 
partly  on  its  content  of  organic  matter.  Featy 
ami  humus  soils,  other  things  being  equal,  have 
the  highest  capacity  for  water,  followed  in  order 
by  mai'L,  clay,  loams, and  sand. 
The  hygroscopic  power — -that  is,  the  power  of 
attracting  water  vapour — is  of  practical  im- 
j)ortance,  in  that  it  prevents  undue  evaporation, 
and  prevents  the  soil  from  becoming  parched  up. 
It  also  serves  as  a guide  to  the  absorptive  power 
for  other  gases.  This  property,  like  capillarity,  is 
due  entirely  to  the  fineness  of  texture,  and  the  order 
is  tlie  same— humus,  clay,  loam,  marl,  sand,  and 
coarse  saua. 
The  absorptive  power  of  the  soil  for  salts  is  a 
factor  of  very  great  importance  in  determining  the 
fertility  of  a soil. 
This  power  which  soils  possess  of  removing 
saline  matter  from  solution,  and  retaining  it  within 
their  pores,  is  due  partly  to  the  chemical  nature  of 
tlie  soil,  resulting  in  a chemical  interchange  of 
basic  constituents,  and  partly  to  its  mechanical 
structure,  the  fineness  of  its  texture,  substances 
such  as  humus  and  clay  {.ossessing  the  power  in  a 
remarkable  degree. 
This  properly  is  determined  by  a method  elabor- 
ated by  Xnop. 
The  absolute  weight  of  the  soil,  though  it  has  no 
bearing  upon  its  fertility,  is  a point  that  should 
always  be  taken  into  account,  since  a heavy,  sandy 
soil,  though  it  may  contain  a smaller  percentage 
of  fertilising  material  than  a light  clay  soil, 
presents  a larger  mass  to  the  plant  in  the  same 
space. 
We  now  come  to  the  most  important  property 
po.sse.ssed  by  soils  as  affecting  their  fertility,  and, 
at  the  same  time,  the  most  obscure,  namely,  their 
power  of  nitrification.  This  property  depends 
upon  a number  of  .points,  on  some  of  which  our 
information  is  not  very  clear. 
From  what  we  know  of  the  process  of  nitrifica- 
tion, we  can  lay  down  with  tolerable  certainty  the 
following  conditions  as  being  favourable  to  the 
process  :— 
We  must  have  free  access  of  air  and  moisture  a 
certain  degree  of  warmth,  the  presence  of  nitro- 
genous organic  matter,  prone  to  oxidation  (re- 
presented by  humus).  The  presence  of  reducible 
mineral  matter,  such  as  se.squioxide  of  iron  or 
metallic  sulphates,  i.s  also  favourable.  A suffi- 
ciency of  basic  subtances  to  combine  with  the 
nitric  acid  appears  also  to  he  advantageous  to 
nitrification. 
Putting  on  one  side  the  bacteriological  aspect  of 
the  phenomena  involved,  we  shall  find  that  the 
formation  of  nitrates  within  the  soil  is  due  to 
oxidation,  and  that  within  certain  limits  the  powder 
of  oxidation  which  the  soil  possesses  is  also  the 
measure  of  its  nitrifying  power. 
We  are,  therefore,  1 believe,  justified  in  assum- 
ing that  the  soil  will  be  most  favourable  to  the 
development  of  the  nitric  ferment  which  combines 
the  following  characteristics  : — 
1st.  A fair  proportion  of  humus. 
2nd.  A warm  climate. 
3rd.  Provision  for  free  access  of  air  and  of 
moisture  (these  depend  upon  its  porosity,  and  are 
determined  by  its  capillary  power). 
4th.  Good  drainage  to  prevent  stagnant  water 
accumulating. 
