178 
'rochleder's  proximate  analysis. 
very  great  mass  of  material  must  be  operated  upoa  to  obtain  the  constituent 
which  is  present  in  small  quantity,  because  from  a  smaller  quantity  of  the 
material  we  cannot  obtain  enough  to  arrive  at  a  conclusion  upon  its  nature 
by  a  suitable  research.  If  we  abstract  from  the  weight  of  a  substance  under 
examination  the  weight  of  water  which  it  contains,  also  that  of  the  inor- 
ganic constituents  and  the  weight  of  cellulose  which  remains  after  the  ma- 
terial has  been  treated  with  ether,  alcohol,  water,  diluted  acids,  and  alkalies, 
we  obtain  an  inconsiderable  residue,  which  represents  all  the  other  bodies 
together  present,  except  the  cellulose,  water,  and  inorganic  constituents.  As 
a  general  rule,  we  seldom  find  more  than  300  grains  of  these  bodies  in  from 
3  lbs.  to  5  lbs.  of  the  crude  material,  which  must  be  subjected  to  a  close  in- 
vestigation if  we  would  arrive  at  a  correct  view  of  their  true  nature.  From 
this  general  estimate,  it  will  be  seen  that  5  lbs.  of  crude  material  is  a  quan- 
tity that  scarcely  is  sufficient  at  any  time  for  the  completion  of  an  analysis. 
The  least  quantity  of  material  is  required  in  those  cases  where  the  known, 
easily  recognized  constituents  are  in  the  smaller  quantity,  and  the  unknown 
ones,  on  the  contrary,  are  in  the  greater  quantity. 
Section  3. — Treatment  of  materials  with  various  solvents. 
The  material  mechanically  prepared  for  the  investigation  should  be  di- 
vided into  several  parts,  and  each  part  treated  with  a  solvent  to  obtain  a 
number  of  extraijts,  which  are  to  be  submitted  to  a  further  examination. 
The  fluids  most  frequently  used  for  a  long  time  for  this  purpose  are  ether, 
alcohol,  and  water  ;  the  latter  is  often  mixed  with  acids  or  alkalies.  The 
ether  is  generally  used  in  a  perfectly  pure  condition,  the  alcohol  mixeJ 
with  more  or  less  water,  according  to  the  strength  of  the  spirit  required. 
Experience  has  shown  that  water,  after  it  has  extracted  bodies  from  a  mate™ 
rial  which  are  quite  soluble  in  water,  also  possesses  the  power  of  dissolv- 
ing substances,  as  already  mentioned,  which  are  either  insoluble,  or  diffi- 
cultly soluble  per  se  therein.  This  disadvantageous  circumstance  occurs 
less  with  alcohol,  and  still  less  with  ether.  In  consequence,  it  has  become 
a  general  rule  to  treat  the  material  first  with  ether,  then  with  alcohol,  and 
lastly  with  water,  when  it  is  intended  to  treat  it  with  these  three  solvents, 
I  have  found  it  the  most  convenient  to  extract  a  portion  of  the  material 
with  hot  water,  another  portion  with  cold  water,  a  third  portion  with  acid- 
ulated water,  a  fourth  portion  with  ammoniacal  water,  a  fifth  portion  with 
alcohol,  and  to  treat  a  sixth  portion  with  ether.  In  peculiar  cases,  a  treat- 
ment with  alcohol  containing  ammonia  or  potash  is  suitable.  The  prepara- 
tion of  these  solutions,  as  well  as  the  precautions  to  be  therein  observed, 
wiH  here  be  more  minutely  discussed. 
I. — 'Treatment  of  tJie  substance  under  examination  with  hailing  water. 
The  treatment  with  boiling  water,  as  previously  stated,  should  afford  us 
a  decoction  and  a  distillate,  of  which  the  former  will  contain  the  non-vol- 
atile constituents  and  the  non-volatile  compounds  of  the  volatile  bodies  in 
