rochleder's  proximate  analysis. 
81 
(Continued  fiom  page  568,  Vol.  ix.) 
the  other  constituent  which  forms  with  oxide  of  lead  an  insoluble  com. 
pound  may  be  a  copulated  compound.  In  the  examination  of  the  frac- 
tional parts  which  were  prepared  from  this  precipitate  according  to  the 
method  described  at  page  373,  vol.  ix.,  attention  should  be  directed  to  this 
point,  and  the  method  should  be  employed  with  hydrochloric  acid  and 
baryta  (or  soda,  or  potash)  as  described  at  pages  469,  561. 
In  the  same  manner  as  directed  for  the  residue  which  is  obtained  from 
the  watery  decoction  treated  with  sugar  of  lead,  subacetate  of  lead,  and 
sulphuretted  hydrogen,  is  the  residue  dealt  with  which  remains  when  the 
watery  decoction  was  filtered  through  animal  charcoal  previous  to  its  treat- 
ment with  the  lead  salts,  and  also  the  residue  which  remains  behind  after  the 
precipitation  of  the  watery  decoction  with  alum  and  ammonia,  evaporat- 
ing and  extracting  with  alcohol,  and  distilling  off  the  alcohol.  Thus  we  have 
in  these  three  examinations  a  mutual  control  of  the  correctness  of  the  re- 
sults obtained  by  each  individual  examination,  and  consequently  a  con- 
stituent can  scarcely  be  overlooked,  and  also  conclusions  may  be  drawn 
on  the  nature  of  the  individual  constituents. 
II. — Examination  of  the  cold  watery  infusion. 
This  fluid,  prepared  in  the  manner  given  at  page  180,  is  divided  into 
several  parts. 
The  first  part  is  introduced  into  a  test  tube,  placed  in  a  beaker  glass 
filled  with  water,  and  the  water  slowly  heated.  By  means  of  a  thermometer 
inserted  in  the  test  tube,  the  temperature  is  observed.  At  a  certain  heat 
a  coagulation  of  one  or  the  other  constituent  is  produced.  When  the  coagu- 
lation of  the  substance  is  noticed,  the  lamp  is  removed  from  under  the 
beaker  glass,  or  the  latter  is  taken  from  the  sand-bath  on  which  it  has 
been  placed  to  heat  it.  The  object  of  this  removal  is  to  prevent  the  tem- 
perature of  the  fluid  in  the  test  tube  rising  any  farther,  and  to  retain  it 
some  time  at  the  same  heat,  or  rather  to  cool  very  slowly.  The  coagulum 
is  separated  after  the  fluid  has  cooled  by  the  filtration  of  the  fluid.  To  pro- 
mote the  filtration,  it  is  better  to  take  a  number  of  small  filters  instead  of 
a  larger  one,  because  the  pores  of  the  filter  are  quickly  stopped  by  coa- 
gulated material  of  that  kind,  and  the  filtration  then  proceeds  extremely 
slowly. 
The  filtrate  is  again  treated  as  the  original  fluid,  only  the  temperature 
is  allowed  in  this  second  treatment  to  rise  more  quickly  to  the  point  where 
the  separation  takes  place,  and  then  slowly  elevated.  The  fluid  heated 
some  degrees  higher  often  throws  off  a  fresh  coagulum,  which  is  likewise 
collected  on  a  filter.  The  filtrate  is  again  heated,  to  see  whether  by  a  still 
higher  temperature  a  third  coagulum  makes  its  appearance.  As  all  coa- 
gulable  substances  do  not  lose  their  solubility  in  water  at  the  same  tem- 
perature, several  of  these  bodies  may  be  separated  from  one  another  when 
they  are  simultaneously  present  in  an  aqueous  extract. 
6 
