-^"AiXisso"""}        Proximate  Analysis  of  Plants,  2  f  3 
Always  determine  the  amounts  removed  by  the  above  treatment  by  weighing  the 
dried,  undissolved  residues.  The  ash,  as  thus  estimated,  usually  inludes  a  little 
imconsumed  carbon,  together  with  more  or  less  carbonic  anhydride  (CO,^),  most,  or 
ail,  of  which  was  not  originally  present  in  the  plant,  but  was  produced  by  the  com- 
^justion  of  the  organic  matter.  For  most  purposes  it  is  unnecessary  to  estimate  and 
■exclude  from  the  ash  this  carbonic  anhydride  5  where  great  accuracy  is  desired,  a 
complete  quantitative  analysis  should  be  made,  the  amount  of  each  base  and  acid 
l5eing  determined,  and  in  the  statement  of  results  only  those  should  be  included 
which  existed  originally  in  the  plant.  For  this  purpose  it  is  necessary  to  burn  from 
twenty  to  one  hundred  grams  of  the  sample  5  for  further  directions  consult  text- 
books on  agricultural  and  inorganic  analysis. 
IV.  Estimation  of  Total  Nitrogen. 
In  half  a  gram  or  more  of  the  sample  determine  total  nitrogen  by  combustion 
with  excess  of  soda-lime,  as  directed  by  Prof.  S.  W.  Johnson  and  E.  H.  Jenkins. 
If  later  in  the  analysis  no  other  nitrogenous  substances  are  discovered,  calculate  the 
total  amount  of  nitrogen  to  albuminoids  by  multiplying  by  6'25.  When  other 
nitrogenous  compounds  are  present,  their  content  of  nitrogen  should  be  determined 
directly  or  by  difference ;  after  proper  deductions  have  been  made,  the  remaining 
nitrogen  should  be  calculated  to  albuminoids. 
V.  Estimation  of  Benzol  Extract. 
In  a  suitable  apparatus  for  repercolation  completely  exhaust  five  grams  of  the 
sample  with  pure  coal-tar  benzol  (sp.  gr.  85 — 88,  boils  at  80  to  85°C.,  leaves  no  residue 
^vhen  evaporated).  The  extraction  requires  from  four  to  six  hours'  continued  action 
of  the  solvent.  Carefully  evaporate  this  liquid  to  dryness  in  a  weighed  dish,  and 
record  its  weight  as  total  benzol  extract.  This  extract  may  contain  volatile  oils  and 
other  aromatic  compounds,  resins,  camphors,  volatile  or  non-volatile  organic  acids, 
wax,  solid  fats,  fixed  oils,  chlorophyll,  other  colors,  volatile  or  fixed  alkaloids,  giuco- 
sides,  almost  no  ash. 
To  the  weighed  extract  add  water,  again  evaporate  on  the  water-bath,  and  com- 
plete the  drying  in  an  air-bath  at  i  ro°C.  In  absence  of  other  vaporizable  substances 
the  loss  of  weight  approximates  the  amount  of  volatile  oil.  If  the  presence  of  a 
volatile  alkaloid  is  suspected  (from  a  characteristic  odor  or  an  alkaline  reaction), 
add  a  drop  of  hydrochloric  acid  to  prevent  its  volatilization  Camphors  are  partially 
dissipated  by  this  treatment  5  hence,  when  they  are  present,  this  evaporation  should 
be  dispensed  with. 
Treat,  now,  the  residue  with  a  moderate  amount  of  warm  water,  allow  to  stand 
until  cool,  then  filter  through  fine  paper  by  aid  of  a  Bunsen's  pump.  In  half  of  the 
aqueous  filtrate  determine  total  organic  matter  and  ash test  the  remaining  half  for 
■alkaloids ^  glucosides  and  organic  acids  by  salts  of  lead,  silver,  barium  and  calcium. 
Care  must  be  taken  not  to  mistake  a  slight  amount  of  suspended  matter,  frequently 
•resinous,  for  other  substances  actually  soluble  in  water. 
The  still  undissolved  residue  should  be  again  removed  from  filters  and  dishes  by 
^solution  in  benzole,  the  benzole  solution  being  again  evaporated  to  dryness.  Treat 
this  residue  with  warm,  very  dilute  hydrochloric  acid,  allow  to  cool,  and  filter 
1  "  Report  Conn.  Agric.  Exp.  Station,"  1878;  "  Clieni.  News,"  July  18,  1879,  p.  28  ;  "  Amer.  Chem, 
Jcurnal,"  i,  p.  77. 
