180 
rochleder's  proximate  analysis. 
dissolves  in  the  water,  while  the  ferment  is  converted  into  an  inactive  con- 
dition. 
With  materials  which  contain  easily  oxidizable  constituents  it  may  be 
readily  perceived  that  by  the  introduction  of  the  substances  into  boiling 
water  their  oxidation  takes  place  in  a  much  smaller  degree  than  by  being 
immersed  in  cold  water  and  subsequently  heated.  The  decoctions  which 
are  obtained  according  to  the  method  here  recommended  are  on  that  ac- 
count generally  much  paler  than  those  produced  by  gradual  heating. 
When  the  substance  to  be  extracted  has  been  sufficiently  long  in  con- 
tact with  the  boiling  water,  and  no  more  volatile  products  can  be  detected 
in  the  distillate,  in  case  such  have  been  formed  therein  at  the  commence- 
ment of  distillation,  the  operator,  after  the  neck  has  been  removed,  with- 
draws the  cylinder  and  its  contents,  places  it  on  a  capacious  dish  or  basin 
to  catch  tlie  droppings,  and  presses  the  material  in  a  press  between  two 
vertical  plates.  The  decoction  ia  filtered,  whilst  hot;,  through  paper.  To 
prevent  it  cooling  while  being  filtered,  as  large  a  number  of  funnels  as  are 
necessary  should  be  employed.  If,  in  consequence  of  the  liquid  cooling, 
anything  should  be  separated  by  the  filter  which  had  been  previously  dis- 
solved, the  filtration  must  be  performed  by  means  of  a  hot  water  funnel. 
From  a  watery  decoction  of  the  flower-buds  of  capparis  spinosa,  the  quer- 
citrine,  or  the  so-called  rutinic  acid,  is  precipitated  by  cooling  in  volumin- 
ous flocks.  The  distillate  thus  obtained  is  either  pure  water,  in  those  cases 
where  the  substance  under  examination  did  not  contain  bodies  distillable 
with  the  vapor  of  water,  or  such  as  are  not  in  a  free  condition,  but  in  the 
form  of  non-volatile  compounds,  or  there  are  volatile  bodies  dissolved 
therein  or  suspended  with  others.  The  distillate  is  then  either  clear  when 
the  volatile  substances  are  readily  soluble  in  the  water  distilled  over  with 
them,  or  are  present  in  very  small  quantity,  or  it  is  turbid  from  suspended 
undissolved  substances  which  exist  in  the  fluid  either  in  the  form  of  oily 
globules,  or  crystals,  but  seldom  in  the  form  of  flocks.  More  frequently, 
when  the  material  contains  a  considerable  quantity  of  volatile  substances 
which  are  not  readily  soluble  in  water,  an  oily  film  swims  on  the  surface 
of  the  distillate,  or  collects  at  the  bottom  of  the  liquid.  The  volatile  bodies 
which  may  be  dissolved  or  suspended  in  the  distillate  belong  often  to  the 
most  different  classes  of  bodies.  Volatile  bases,  volatile  acids,  hydro- 
carbons, indifferent  volatile  oils  containing  oxygen,  aldehydes,  compound 
ethers,  may  be  contained  in  such  a  distillate.  It  is  a  rare  case  for  only 
one  volatile  substance  to  be  found  by  a  close  examination  of  the  distillate. 
If  the  substance  under  examination  contains  only  small  quantities  of  vola- 
tile substances,  recourse  must  be  had  to  cohobation.  When  a  portion  of 
the  material  has  been  treated  in  the  manner  directed,  and  a  sufficient 
quantity  of  the  distillate  has  been  obtained  to  point  out  by  means  of  a 
preliminary  examination  to  what  classes  of  bodies  the  volatile  substances 
found  therein  belong,  it  may  be  easily  determined  whether  cohobation  ia 
necessary  or  not.    Assuming  there  were  only  volatile  acids  or  volatile 
