180 
rochleder's  proximate  analysis. 
method  of  examination,  on  the  contrary  it  will  happen  in  many  cases  that 
this  prescribed  method  is  not  the  best,  and  ^must  be  replaced  by  another 
which  renders  possible  the  separation  of  bodies,  which  cannot  be  accom- 
plished with  the  same  precision  in  the  method  given.  Particularly  when 
coloring  matters  are  contained  in  the  spirituous  extract,  their  isolation  by 
the  methods  already  prescribed  cannot  be  performed  quickly  or  perfectly. 
In  such  cases,  the  hydrate  of  alumina  is  often  employed  with  remarkable 
results  for  a  preliminary  separation  of  the  constituents.    This  is  prepared 
by  precipitating  a  solution  of  alum  with  sulphide  of  ammonium,  the  pre- 
cipitate is  washed  at  the  commencement  by  decantation,  and  then  washed 
on  a  filter  with  water,  and  removed  from  the  filter  in  a  moist,  gelatinous 
condition.    It  can  be  preserved  in  closed  vessels  for  use  in  a  moist  condi- 
tion, or  at  once  employed  ;  the  gelatinous  hydrate  is  rubbed  with  water, 
which  is  added  by  degrees  in  small  quantities,  to  a  smooth  thin  paste. 
This  is  added  to  the  watery  fluid  which  has  been  obtained  after  the  distil- 
lation of  the  spirit  from  spirituous  extract  of  the  material  under  examina- 
tion, and  after  the  removal  of  the  fatty  and  resinous  deposits  by  filtration, 
the  hydrate  of  alumina  is  diffused  equally  through  the  fluid  by  stirring, 
and  allowed  to  remain  in  contact  twenty-four  hours,  with  frequent  stirring. 
At  the  expiration  of  this  time  the  fluid  is  filtered  from  the  alumina,  which 
is  washed  on  a  filter  with  water;  the  filtered  liquid,  as  well  as  the  alumina 
on  the  filter  are  subjected  to  further  examination.    There  are  bodies  which 
combine  with  alumina,  and  others  which  form  no  combination  with  it. 
The  bodies  which  can  combine  with  alumina  are  on  the  filter  with  the 
alumina,  which  has  been  added  in  excess,  in  the  form  of  salts  of  alumina, 
or  are  retained  by  the  alumina  in  the  same  way  that  many  bodies  are  fixed 
by  charcoal  or  sulphide  of  lead.    TJie  mixture  of  alumina  and  alumina  com- 
pounds is  treated  precisely  as  the  alumina  precipitate  which  has  been  ob- 
tained by  the  alum  and  ammonia  from  the  watery  decoction.    The  liquid 
which  is  filtered  from  the  alumina  and  its  compounds  is  precipitated  with 
subacetate  of  lead  ;  this  precipitate  is  separated  from  the  fluid  by  filtration, 
the  fluid  from  the  lead  by  sidphuretted  hydrogen,  and  freed  from  the  sul- 
phuretted hydrogen  by  heat  after  the  sulphuret  of  lead  has  been  filtered  off. 
This  lead  precipitate,  and  the  fluid  filtered  therefrom,  are  treated  like  the 
corresponding  fluid  and  precipitate  were  treated  when  no  alumina  had 
been  previously  added  to  the  aqueous  residue  of  the  spirituous  extract. 
Frequently,  in  the  spirituous  extract  there  are  two  coloring  matters  present, 
one  of  which  has  the  nature  of  a  resin.     Such  coloring  matters  separate 
cotemporaneously  with  the  fats  and  resins,  when  the  spirit  is  distilled  from 
the  extract,  and  they  are  isolated  in  the  examination  of  the  resins.  Many 
coloring  matters  remain  dissolved  in  the  water  after  the  spirit  is  distilled 
off.    This  case  often  occurs  that  one  of  the  coloring  matters  is  completely 
combined  and  retained  by  the  freshly-precipitated  alumina,  with  other  bo- 
dies, when  a  sufficient  quantity  of  alumina  has  been  added  to  the  fluid, 
while  the  other  coloring  matter  remains  behind  in  the  fluid.    The  latter  is 
