182 
rochleder's  proximate  analysis. 
carbon,  to  ascertain  whether  a  separation  can  be  thereby  effected  into  two 
parts.  If  no  separation  is  possible,  the  ivhole  residue  left,  after  treating  the 
remaining  'portion  of  the  ethereal  extract  with  water,  is  treated  ;  or  when  a 
separation  has  been  accomplished,  by  sulphuret  of  carbon  ;  then  the  por- 
tion insoluble  in  sulphuret  of  carbon  by  itself,  and  the  portion  which  re- 
mains after  distilling  off  the  sulphuret  of  carbon  by  itself,  are  treated  as 
described  for  the  mixture  of  fats  and  resins,  which  is  obtained  from  the 
material  under  examination  by  extraction  with  spirit,  and  cooling  the 
tincture,  or  by  distilling  off  the  alcohol.    (See  pages  84  to  179.) 
Yil. — Examination  of  the  matter  extracted  by  spirit  containing  potash 
or  ammonia. 
The  solution  which  is  obtained  by  spirit  containing  potassa  or  ammonia 
is  sometimes  very  suitable  for  the  isolation  of  substances  which  could  only 
be  procured  with  difficulty  in  a  pure  condition  from  the  material  under  ex- 
amination in  another  way.  The  substances  whose  isolation  may  be  at- 
tempted from  this  solution  are  those  which  are  sparingly  soluble  in  very 
diluted  alcohol,  but  are  dissolved  in  considerable  quantity  by  potassa  or 
ammonia,  so  that  the  greatest  portion  of  them  is  separated  by  an  acid, 
while  others  extracted  at  the  same  time  are  not  precipitated  after  the  addi- 
tion of  an  acid,  because  they  are  soluble  likewise  in  their  free  state,  in  very 
dilute  alcohol.  Frequently,  ca.rbonie  acid  suffices  to  decompose  the  com- 
pounds of  these  substances  with  potash  or  ammonia,  so  that  carbonate  of 
potash  and  the  substance  which  was  combined  with  the  alkali  are  together 
separated.  Sometimes  stronger  acids,  as  acetic,  sulphuric,  or  hydrochloric 
acid,  are  necessary  for  the  decomposition.  At  first,  therefore,  carbonic  acid 
is  always  conducted  into  the  alkaline  spirituous  extract,  to  see  whether  a 
precipitation  of  organic  substance  takes  place.  When  this  is  the  case,  the 
precipitate  is  filtered  from  the  fluid  and  examined  more  closely.  The  fil- 
tered fluid  is  mixed  then  with  hydrochloric  acid,  to  ascertain  whether  a 
precipitate  is  thereby  produced.  In  this  way  it  is  possible  to  separate  one 
or  more  weaker  acids  from  stronger  ones.  The  precipitates  produced  by 
hydrochloric  acid  must  be  separated  by  filtration  from  the  fluid,  which  is 
not  further  examined.  Various  peculiar  bodies  are  readily  obtained  in 
this  way  pure;  for  example,  chrysophanic  acid  from  rhubarb  and  parmelia 
parietina,  also  usnic  acid  and  analogous  bodies  from  many  lichens.  The 
preparation  of  these  bodies  is  in  no  other  way  so  easily  and  rapidly  per- 
formed as  in  this  manner.  Naturally  the  precipitates  produced  by  hydro- 
chloric acid,  as  well  as  by  carbonic  acid,  may  be  not  only  one  substance, 
but  a  mixture  of  several  bodies,  and  it  is  therefore  necessary  to  learn 
whether  by  treatment  with  alcohol,  ether  and  water,  a  separation  is  possible 
or  not  into  several  constituents.  When  it  is  not  possible  to  effect  a  separa- 
tion of  the  mixed  bodies,  by  their  unequal  solubility  in  these  solvents, 
then  a  solution  of  the  mixture  is  made  in  that  menstruum  which  most  readily 
effects  its  solution,  such  as  ammoniacal  water  or  ammoniacal  spirit,  and 
