ON  SOME  CONSTITUENTS  OF  RHUBARB. 
448 
and  of  amyl-alcohol,  as  the  best  suited  for  the  purpose.  The 
deposit  of  the  "  Tinctura  Rhei"  parts  readily  with  its  chryso- 
phane  when  treated  in  a  finely-powdered  state  with  benzol  (puri- 
fied coal-tar  naphtha  may  be  substituted,)  in  a  Mohr's  extraction 
apparatus.  In  order  to  prepare  chrysophane  from  rhubarb 
itself,  a  preliminary  operation  is  necessary ;  the  crushed  root 
must  be  previously  macerated  with  cold  water,  which  removes 
more  than  50  per  cent,  of  soluble  matter ;  these  not  only  neces- 
sarily increase  the  bulk  of  material  to  be  operated  on,  but  they 
also  render  the  extraction  of  the  chrysophane  much  more  diffi- 
cult. After  maceration  with  water,  the  root  is  dried  and  treated 
with  benzol  in  a  Mohr's  apparatus.  By  operating  in  the  manner 
described,  a  very  concentrated  solution  of  chrysophane  is  ob- 
tained, and  a  comparatively  small  quantity  of  the  solvent  is 
employed. 
The  fact  that  chrysophane  is  but  slightly  soluble  in  alcohol, 
and  much  less  so  in  the  dilute  alcohol  employed  in  the  prepara- 
tion of  the  tincture  of  rhubarb,  led  to  the  conjecture  that  the 
greater  part  of  the  chrysophane  remains  in  the  residuary  root. 
An  experiment,  carried  out  with  such  residuary  rhubarb  as  is 
thrown  away  in  pharmaceutical  laboratories,  proved  this  conjec- 
ture to  be  well  founded,  as  the  residue  furnished  2.6  per  cent,  of 
chrysophane.  It  is,  indeed,  better  suited  for  treatment  with 
benzol  than  the  original  root,  in  consequence  of  its  not  being 
necessary  to  macerate  it  previously  with  water. 
The  benzolic  solution  obtained  from  either  of  the  above-named 
sources  is  concentrated  by  distilling  off  the  greater  part  of  the 
benzol ;  on  cooling,  the  solution  becomes  nearly  solid  by  depos- 
iting the  crude  chrysophane.  The  mother-liquor  contains  ery- 
throretin  and  a  neutral  fat,  and  it  is  advisable  to  sacrifice  the 
small  quantity  of  chrysophane  retained  in  the  mother-liquor,  by 
at  once  pressing  the  crude  chrysophane  between  the  blotting- 
paper. 
On  re-dissolving  the  crude  chrysophane  in  hot  benzol,  a  reddish- 
yellow  and  much  less  soluble  body  is  left  undissolved,  and  the  hot 
of  benzol ;  guaiacic  acid  can  also  be  separated  by  its  means  from  gum 
guaiacum,  the  benzol  dissolving  the  acids  and  leaving  the  gum  unacted 
upon ;  on  evaporation,  the  acids  are  obtained  at  once  in  remarkably  fine 
crystals. 
