^'"aS'is^o!''"'"}       Proximate  Analysis  of  Plants,  2 1 9 
day.  Flter  through  fine  linen,  or  Gooch's  filter,  wash  with  hot  water,  dry  at  no  to 
i2o°C.,  and  weigh,  ash  free,  as  cellulose.  The  loss  of  weight  by  this  treatnnent  state 
as  lignose  and  color. 
Remarks. 
It  is  advisable  to  determine  always,  in  addition  to  what  has  already  been  directed, 
the  amounts  extracted  directly  from  the  sample  by  water,  ether,  alcohol  of  various 
percentages,  methylic  alcohol,  naphtha,  chloroform,  carbon  disulphide,  etc.  In  each 
extract  estimate  total  organic  matter  and  ash,  determine  qualitatively,  and  quantita- 
tively when  possible,  its  constituents,  by  treating  with  such  solvents  and  reagents  as 
are  indicated.  Each  extract  being  composed  of  certain  distinct  substances,  it  is 
necessary  to  account  for  them  in  every  case. 
The  amounts  present  of  some  constituents  may  be  found  by  subtracting  the  weight 
extracted  by  some  one  solvent  from  the  weight  extracted  by  some  other.  It  will  be 
seen  that  this  is  a  method  of  limited  applicability,  which  can  only  be  applied  in  those 
cases  where  the  difference  between  the  solvent  action  of  the  two  liquids  is  very 
sharply  defined.  Certain  special  methods  for  the  estimation  of  single  constituents 
may  be  used,  care  being  taken  that  all  interfering  substances  be  first  removed.  The 
methods  of  preparation  of  known  substances  as  given  in  Husemann's  "  Pflanzen- 
stolfe,"  and  to  a  considerable  extent  in  Watt's  Dictionary,  may  serve  as  suggestions  tor 
work.  Treatment  with  benzol,  eighty  per  cent,  alcohol,  and  water,  removes  from 
nearly  all  plants  the  constituents  of  greatest  chemical  and  medicinal  interest,  but  in 
analyses  of  grains,  fodder  and  food  materials  those  compounds  extracted  by  dilute 
acids  and  alkalies  have  great  value.  There  are  substances  in  plants,  seemingly  iso- 
mers of  starch  and  cellulose,  which  have  properties  more  or  less  resembling  those  ot 
cellulose,  and  are  changed  by  boiling  with  dilute  acids  to  glucose.-  In  absence  of  an 
established  nomenclature  it  has  seemed  best  to  use  the  terms  "starch  isomers/'  or 
"amylaceous  cellulose"  for  these  substances,^  while  those  constituents,  not  albumin- 
ouSy  which  are  removed  by  dilute  alkali  have  been  termed  "alkali  extract."  These 
substances  have  been  investigated  by  various  chemists,  but  no  definite  and  authori- 
tative nomenclature  has  yet  been  adopted.  Thomsen  gives  the  name  "  holz-gum- 
mi,"^  nvood gum,  to  a  white  substance  extracted  from  plants  by  dilute  sodic  hydrate, 
while  Fremy  regards  these  various  compounds  as  modifications  of  pectic  acid,  pectin, 
and  "cellulose  bodies."^  Starch  also  may  exist  in  some  seeds  (as  of  sweet  corn)  in 
a  form  soluble  in  water. ^ 
It  will  be  seen  that  the  field  for  investigation  is  limitless,  and  almost  unoccupied 
as  yet,  and  that  there  is  great  need  for  improved  methods  for  proximate  analysis. 
The  analyst  will  find  that  a  study  of  any  common  plant  will  require  of  him  much 
more  than  unthinking,  mechanical  habits  of  manipulation,  while  every  careful 
investigation  will  reveal  to  him  some  constituents  deserving  more  full  and  accurate 
study. 
^  U.  S.  Dept.  of  Agric.  Report,  1878,  p.  189. 
2  Kolbe's  "Jour.  prak.  Chem."  Band  19,  p.  146. 
^  "Compt.  Rend."  Ixxxiii,  1136;  "Jour.  Chem.  Soc."  1877,  p.  229. 
^U.  S.  Dept.  of  Agric.  Report,  1878,  pp.  153—155. 
