aS'iss'o!'"'"  }       Proximate  Analysis  of  Plants,  ^  217 
4.  In  20  cc.  of  the  aqueous  solution  determine  tannin  gravimetrically  by  A. 
Carpeni's  method  ;i  precipitate  by  ammoniacal  acetate  of  zinc,  use  a  Gooch's  filter, 
wash  the  precipitate  with  very  weak  ammonia,  dry  at  i2o°C.,  weigh,  ignite  cau- 
tiously, again  weigh.  The  loss  by  ignition  equals  tannic  acid,  in  absence  of  certain 
interfering  substances. 
5.  Precipitate  20  cc.  by  normal  acetate  of  lead,  and  determine,  as  before  described, 
the  amount  of  organic  matter  after  drying  at  100  to  i2o°C.  This  precipitate  will 
contain,  if  the  substances  are  present  in  the  plant,  tannic^  gallic,  and  most  other 
organic  acidsy  some  colors,  rarely  albumitious  substances,  some  extracti^ues,  and  most 
inorganic  acids  of  the  ash.  Determine,  by  difference,  the  amount  not  precipitated 
by  this  treatment. 
6.  In  20  cc.  de.termine  in  like  manner  the  amount  precipitated  by  basic  acetate 
("  subacetate")  of  lead.  This  reagent  precipitates  a  greater  number  of  acids,  colors 
and  extractives  than  are  precipitated  by  the  normal  acetate,  hence  it  is  frequently 
possible  to  estimate  such  substances  by  subtracting  the  amount  precipitated  by  one 
reagent  from  the  amount  precipitated  by  the  other.  To  the  filtrate  add  a  slight 
excess  of  dilute  hydrochloric  acid,  boil  gently  for  half  an  hour,  and  determine  in 
the  liquid  total  glucose  by  use  of  Fehling's  solution. 
7.  Precipitate  20  cc.  by  subacetate,  exactly  as  in  6,  and  use  the  precipitate  as  a 
duplicate  to  check  the  amount  there  estimated.  To  the  filtrate  add  a  very  slight 
excess  of  solution  of  carbonate  of  sodium,  filter  from  the  carbonate  of  lead,  wash 
well  with  water  containing  a  little  alcohol,  and  in  the  filtrate  estimate  actual  glucose. 
If  the  glucose  thus  found  is  appreciably  less  than  that  in  6,  subtract  it  from  that 
amount  5  this  glucose  may  be  due  to  the  presence  in  the  plant  of  sucrose  or  some 
glucoside.  If  due  to  sucrose,  the  amount  of  the  latter  may  be  found  by  multiplying 
this  residual  glucose  by  '95  5  if  to  a  glucoside,  a  fit  subject  for  an  extended  investi- 
gation is  presented.  The  properties,  formula  and  decomposition  products  of  the 
newly-found  glucoside  should  be  carefully  studied. 
8  Precipitate  20  cc.  with  subacetate  of  lead,  as  in  6  and  7,  employing  the  pre- 
cipitate as  material  from  which  to  separate  organic  acids,  after  removal  of  lead  by 
mlphuretted  hydrogen.  Acidulate  the  filtrate  with  sulphuric  acid,  add  an  equal 
volume  of  alcohol,  allow  to  stand  two  hours,  filter,  wash  the  precipitate  with  50 
per  cent,  alcohol,  and  evaporate  the  filtrate  until  all  alcohol  has  been  dissipated. 
Test  the  acid  solution  for  alkaloids,  glucosides,  sugars,  extracthues. 
9.  Reserve  the  remaining  40  cc.  for  duplicating  any  unsatisfactory  determinations. 
10  The  residue  mentioned  in  3  as  insoluble  in  water  may  contain  resins,  albu- 
minoids (especially  from  seeds),  colors,  alkaloids,  glucosides.  Dilute  acids  remove 
alkaloids  and  some  glucosides;  dilute  ammonic  hydrate  will  remove  some  r^'/zV/j, 
colors  and  glucosides.  Any  still  insoluble  residue  probably  contains  albuminous  or 
resinous  substances. 
VII.  Estimation  of  Cold  Water  Extract. 
That  part  of  the  plant  remaining  insoluble  after  treatment  with  alcohol  should 
be  dried  at  iio°C.,  and  completely  extracted  by  cold  water.    When  the  plant  con- 
tains considerable  mucilaginous  matter  this  is  best  removed  by  placing  the  sub- 
1  "Chem.  News,"  July  9,  1875,  p.  19,  from  "  Gaz.  Chim.  Ital.,"  1875,  No.  3 ;  "  Proc.  Am.  Ph.  Asso.,' 
75,  P-  341.    See  also  "Amer.  Jour.  Phar.,"  1876,  p.  219. 
