rochleder's  proximate  analysis. 
87 
days  to  a  temperature  between  140°  and  150°  Fahr.,  and  thereby  rendered 
free  from  a  portion  of  their  hygroscopic  water.  The  presence  of  a  fatty 
oil  oftentimes  makes  the  substance  to  be  examined  tenacious  ;  after  the 
expression  of  the  oil  from  the  coarsely  powdered  material,  the  residue  can 
then  be  finely  divided, 
When  resins  or  fats  in  smaller  quantities  are  the  cause  of  the  tenacity 
and  elasticity,  the  comminution  of  substance  may  be  eifected  by  first  re- 
moving, by  a  suitable  solvent,  the  objectionable  portion  of  the  constituents 
from  the  coarsely  powdered  substance,  then  drying  it,  when  it  can  be 
finely  divided. 
The  pulverization  is  always  facilitaced  when  it  is  accomplished  by  stamp- 
ing or  rubbing,  by  separating  the  coarser  from  the  finer  particles  by  means 
of  a  sieve,  and  repeating  the  operation  on  the  coarser  portion. 
Whether  a  substacce  is  to  be  reduced  to  a  fine  state  of  division  by 
stamping,  rubbing,  rasping,  cutting,  or  crushing  between  rollers,  depends 
on  its  properties,  and  no  instructions  can  be  previously  given  here  in  this 
respect.  The  apparatus  required  for  these  operations  are  so  well  described 
in  various  works,  and  rendered  intelligible  by  the  aid  of  engravings  that  it 
appears  superfluous  to  enter  more  closely  into  this  matter. 
Before  the  pulverized  material  is  treated  with  appropriate  solvents,  it  is 
advisable  in  all  cases  to  observe  M^hether  it  is  not  possible  by  expression  to 
completely  separate  certain  constituents.  In  the  investigation  of  vegetable 
substances  which  contain  liquid  fats,  or  fats  fusible  at  a  moderate  tempera- 
ture, a  great  portion  of  the  fat  may  be  separated  by  cold  expression,  or  by 
plates  heated  to  212°  Fahr.  In  the  investigation,  the  advantage  is  not 
only  thereby  gained  that  a  considerable  quantity  of  fat  is  separated  from 
the  other  constituents,  but  many  other  advantages  are  thus  attained  in  the 
further  treatment  of  the  substance — for  example,  in  its  extraction  with 
water  as  well  as  with  alcohol,  as  the  presence  of  a  large  quantity  of  fat  oc- 
oasions  many  inconveniences.  The  watery  decoction,  as  well  as  the 
watery  residue,  which  remains  behind  after  the  expulsion  of  the  alcohol 
from  the  extract  prepared  with  spirit,  is  rendered,  with  materials  rich  in 
fat,  often  turbid,  and  cannot  be  obtained  clear  by  filtration.  With  such 
liquids  the  filtration  proceeds  with  extreme  slowness.  This  disadvantage 
is  everywhere  evident  when  saponin  or  analogous  bodies  are  present  in 
solutions,  which  divide  the  fat  so  finely  and  suspend  it  in  the  liquid,  that 
it  passes  through  a  moist  filter  simultaneously  with  the  liquid.  Even 
when  the  liquid  can  be  obtained  clear  by  filtration,  its  filtration  is  very 
much  retarded  thereby,  and  the  opportunity  to  decompose  is  afforded  to  the 
dissolved  substances.  When  a  turbid  fluid,  containing  fat,  is  mixed  with 
a  saline  solution  to  produce  a  precipitate,  the  precipitate  oiecbanically 
throws  down  the  fat,  becomes  so  pasty  in  consequence,  and  difficultly  divi- 
sible in  water,  that  its  solution  in  acids,  its  decomposition  by  a  current  of 
gas,  and  by  other  agents,  are  very  difiiculfc  to  be  accomplished.    There  often 
