370 
rochleder's  proximate  analysis. 
it  is  noticed  whether  a  small  portion  of  the  fluid  which  has  been  filtered, 
by  further  evaporation  and  cooling  throws  out  more  of  the  bodies  which 
were  separated  hj  the  cooling  of  the  original  decoction.  When  this  is 
the  case,  the  filtered  decoction  is  concentrated  by  evaporation,  to  obtain 
the  principal  bulk  of  such  substances  difficultly  soluble  in  water.  After 
collecting  the  substances  on  a  filter,  the  filtrate  is  treated  as  the  decoction 
would  have  been  treated  if  nothing  had  separated  by  cooling. 
Frequently  the  watery  decoction  contains  a  proportionately  large  quan- 
tity of  slimy  substances,  which  belong  either  to  the  group  of  indifferent 
carho-Jiydraies  or  to  the  class  of  ijectine  compounds.  By  the  presence  of  a 
great  quantity  of  these  bodies,  the  watery  decoction  is  often  so  dense  that, 
when  cold,  it  is  quite  stringy.  These  substances,  without  exception,  are 
insoluble  in  alcohol.  But  even  when  the  decoction  is  not  so  dense,  the 
precipitates  obtained  therefrom  are  mostly  so  voluminous  and  gelatinous 
that  the  fluid  cannot  be  completely  filtered  from  them,  but  is  retained  in 
the  voluminous  gelatinous  flocks.  In  such  cases  these  substances  must  be 
removed.  For  this  purpose  the  decoction  is  concentrated  by  evaporation,  and 
anhydrous  alcohol  is  added  to  the  still  hot  fluid  as  long  as  a  bulky  flocculent 
precipitate  is  thrown  down.  By  filtration  the  fluid  is  separated  from  the 
precipitate.  In  many  instances  alcohol  does  not  produce  a  flocculent 
(precipitate,  but  it  causes  a  considerable  turbidity,  and  the  precipitate  de- 
posits itself  as  a  tenacious  mass  at  the  bottom,  which  is  particularly  the 
case  when  gum  or  an  analogous  body  is  precipitated  by  alcohol  simulta- 
neously with  various  salts  of  organic  acids. 
The  spirituous  fluid  separated  from  the  precipitate  is  subjected  to  dis- 
tillation, which  is  stopped  as  soon  as  all  the  alcohol  has  passed  over,  and 
the  liquid  is  free  from  it.  This  watery  residue  of  the  distillation  is  treat- 
ed precisely  as  the  original  watery  decoction,  when  no  such  gelatinous 
substances,  or  those  rendering  the  fluid  dense  and  tenacious,  were  preci- 
pitated by  alcohol  therefrom. 
This  treatment  is  as  follows: — The  watery  decoction  is  divided  into 
several  parts.  To  one  part  of  the  watery  decoction  is  added  a  concentrated 
cold  aqueous  solution  of  acetate  of  lead,  as  long  as  a  precipitate  is  thereby 
produced.  The  precipitate  is  brought  on  a  filter  and  washed  well  with 
water.  The  liquid  filtered  from  the  precipitate  is  mixed  with  subacetate  of 
lead  as  long  as  anything  is  thrown  down.  This  precipitate  is  likewise^ 
collected  on  a  filter  and  washed  with  water.  The  filtrate  is  freed  from 
the  lead  contained  therein  by  a  stream  of  sulphuretted  hydrogen,  sepa- 
rated from  the  sulphuret  of  lead  by  a  filter,  and  the  sulphuretted  hydrogen 
expelled  by  heating  the  filtrate.  The  sulphuret  of  lead  is  exhausted  with 
hot  water,  and  when  this  takes  nothing  up  it  is  treated  with  hot  alcohol, 
and  the  hot  filtered  solution  is  concentrated  in  a  water-bath.  Frequently 
bodies  which  are  retained  by  the  sulphuret  of  lead  crystallize  out  afcer 
long  standing  from  the  concentrated  aqueous  or  alcoholic  extract.  The 
fluid  precipitated  with  acetate  of  lead  and  snbaeeiate  of  lead,  freed  from  lead 
