rochleder's  proximate  analysis. 
179 
up  into  two  products  one  of  which  is  grape  sugar.  It  is  therefore  proba- 
ble that  not  only  are  other  resins  such  copulated  carbo-hydrates,  but  that 
some  resins  are  compounds,  which,  by  the  action  of  an  acid  or  an  alkali, 
may  be  split  up  into  two  products,  one  of  which  is  not  grape  sugar.  The 
resins  must  in  this  respect  be  more  minutely  examined. 
This  examination  is  conducted  in  the  manner  described  (pages  472,  voL 
ix.,  and  87,  vol.  x.)  for  the  investigation  of  copulated  compounds  with  acids 
and  alkalies. 
It  is  self-evident  that  in  the  presence  of  several  resinous  acids,  their  sepa- 
ration can  be  accomplished  in  the  same  manner  as  this  is  effected  with 
non-resinous  acids,  namely,  by  fractional  precipitation. 
When  the  spirit  is  distilled  off  from  the  alcohol  extract,  and  the  separated 
resins,  fats,  and  wax-like  bodies  are  separated  from  the  watery  residue,  and 
the  watery  fluid  is  freed  from  every  trace  of  suspended  substances  by  a 
moist  filter,  this  watery  solution  is  now  a  subject  for  examination. 
b. —  Watery  residue  after  the  removal  of  the  alcohol  from  the  spirituous  extract 
or  decoction. 
This  fluid  is  diluted  with  a  little  water,  and  precipitated  with  a  solution 
of  sugar  of  lead,  the  precipitate  collected  on  a  filter,  the  filtered  liquid 
mixed  with  basic  acetate  of  lead  as  long  as  a  precipitate  results  ;  and  this 
second  precipitate  is  also  separated  from  the  fluid  by  a  filter.  The  filtered 
liquid  is  freed  from  lead  by  sulphuretted  hydrogen,  from  sulphuret  of  lead, 
by  filtration,  and  from  sulphuretted  hydrogen  by  heating  it.  This  fluid, 
as  well  as  both  the  precipitates  obtained  by  sugar  of  lead  and  subacetate 
of  lead,  are  treated  precisely  as  the  precipitates  and  fluid  were  treated 
which  were  obtained  by  the  corresponding  treatment  of  the  watery  decoc- 
tion of  the  material  to  be  examined. 
It  is  here  to  be  remarked,  that  by  the  examination  of  this  precipitate, 
as  well  as  those  obtained  by  sugar  of  lead  and  subacetate  of  lead,  sub- 
stances will  be  found  which  have  been  also  found  by  the  examination  of 
the  precipitates  obtained  from  the  watery  decoction.  Thus  far,  this  exami- 
nation is  a  control  of  the  previous  one.  However,  these  precipitates  gene- 
rally exhibit  a  less  complicated  composition  than  those  obtained  from  the 
watery  decoction.  The  spirit  does  not  dissolve  many  salts — particularly 
of  the  inorganic  acids,  sulphuric  acid,  phosphoric  acid,  &c.  The  pectine 
bodies  are  quite  as  little  dissolved  by  spirit.  In  the  precipitate  obtained 
by  sugar  of  lead,  certain  bodies  are  therefore  absent  which  are  precipitated 
by  sugar  of  lead  from  the  watery  decoction.  On  the  other  hand,  no  gum 
is  dissolved  by  spirit,  as  well  as  some  allied  substances,  which  would  be 
contained  in  the  watery  decoction,  and  then  would  pass  over  into  the  pre- 
cipitate which  subacetate  of  lead  produces  in  the  watery  decoction.  For 
the  preparation  of  many  bodies  it  is,  therefore,  much  better  to  use  the  pre- 
cipitates which  are  precipitated  from  the  watery  residue  of  the  spirituous 
extract  than  the  corresponding  precipitates  from  the  watery  decoction. 
Although  we  often  obtain  useful  results  by  following  the  prescribed 
