rochleder's  proximate  analysis. 
181 
then  precipitated  with  other  bodies  by  the  addition  of  subacetate  of  lead. 
In  the  majority  of  cases,  the  coloring  matter  is  retained  by  the  sulphuret  of 
lead  after  the  decomposition  of  the  precipitate  by  sulphuretted  hydrogen, 
so  that  it  can  be  extracted  by  hot  alcohol  from  the  sulphuret  of  lead,  after  the 
removal  of  the  other  constituents  by  water. 
Before  concluding  this  chapter,  I  have  to  return  to  the  deposits  from  the 
alcoholic  tincture,  which  in  many  instances  occur  after  the  cooling,  or  after 
the  distillation  of  the  alcohol.  Occasionally,  a  body  or  a  mixture  of  bodies, 
is  separated  in  the  form  of  powders,  which  may  be  readily  collected  upon 
a  filter  for  further  examination.  Smietimes,  however,  no  deposit  takes 
place  after  cooling,  and  after  most  or  all  of  the  alcohol  has  been  distilled  off, 
a  gelatinous  mass  or  a  jelly  is  obtained  after  cooling,  which,  after  having 
been  mixed  with  water,  cannot  be  filtered,  or  at  least  clogs  the  pores  of  the 
filter  in  a  short  time,  thus  stopping  filtration  completely.  There  remains 
no  alternative  in  such  cases,  but  to  add  again  the  distilled  spirit  to  the 
residuary  liquid,  and  to  warm  the  whole,  in  order  to  effect  a  solution  ;  this 
solution  is  then  precipitated  by  a  solution  of  acetate  of  lead  in  hydrated 
alcohol,  the  filtrate  precipitated  by  subacetate  of  lead,  and  the  liquid  filter- 
ing from  this  precipitate,  freed  from  lead  by  sulphuretted  hydrogen.  Both 
precipitates  are  treated  in  precisely  the  same  manner  as  the  precipitates  ob- 
tained by  acetate  and  subacetate  of  lead,  from  the  aqueous  decoction  of  the 
material  under  examination.  The  liquid  which  has  been  freed  from  lead 
by  sulphuretted  hydrogen,  may  contain  substances  which  yield  with  lead 
compounds  soluble  in  alcohol.  The  alcohol  is  therefore  distilled  off,  and 
the  aqueous  residue  is  treated  with  basic  acetate  of  lead,  which  will  pro- 
duce a  precipitate,  if  the  alcoholic  solution  had  contained  lead  compounds 
which  are  insoluble  in  water.  The  liquid  filtered  from  this  precipitate  is 
freed  from  lead  by  sulphuretted  hydrogen,  and  can  now  be  regarded  as 
completely  liberated  from  substances  which  are  precipitated  by  lead;  it  is 
then  further  examined. 
VI. — Examination  of  the  ethereal  extract. 
The  extract  of  the  material  under  examination,  after  the  ether  has  been 
separated  by  distillation  in  a  water  bath,  will  leave  mostly  fats  or  resins, 
or  a  mixture  of  both.  It  frequently  contains  small,  seldom  large  quantities 
of  other  bodies,  which  are  dissolved  equally  by  water  or  spirit,  and  are 
found  in  the  watery  decoction  or  spirituous  extract.  Free  acids,  organic 
bases,  and  various  indifferent  bodies  may  be  taken  up  by  the  ether.  The 
residue  which  remains  after  distilling  off  the  ether  is  consequently  first  boiled 
with  water.  Tannin  and  analogous  bodies,  some  vegetable  bases  and  other 
substances,  are  taken  up  by  the  water,  while  the  fats  and  resins  remain 
undissolved.  The  watery  solution  of  the  ethereal,  extract  is  treated  pre^ 
cisely  as  the  watery  decoction  of  the  material  under  examination.  The 
residue  insoluble  in  water,  after  the  separation  of  all  the  water,  is  submitted 
to  a  further  examination.    A  portion  thereof  is  treated  with  sulphuret  of 
