The  ease  with  which  furfural  can  be  produced  from  pen-
toses has  led  to  the  following  method  of  estimation,  which  is
due  to  Krober  f  : —

A  weighed  quantity  of  substance  %  (usually  about  5  grams)
is  placed  in  a  300  c.c.  flask  provided  with  a  cork  bored  with
two  holes,  through  one  of  which  passes  a  tap-funnel,  and
through  the  other  a  splash  preventor,  such  as  is  used  in  a
Kjeldahl  distillation.  Through  the  tap-funnel  100  c.c.  of
hydrochloric  acid  (sp.  gr.  i '06,  containing  about  12  percent
HCl)  are  then  added,  and  the  contents  of  the  flask  are  dis-
tilled briskly  ;  when  30  c.c.  have  passed  over,  the  distillation  is
interrupted  and  the  contents  of  the  receiver  are  poured  into  a
beaker  with  a  400  c.c.  graduation  mark  ;  a  fresh  quantity  of
30  c.c.  of  hydrochloric  acid  (sp.  gr.  i  '06)  is  now  added  through
the  tap-funnel,  and  the  distillation  is  continued  until  30  c.c.
more  have  distilled  over  ;  the  new  distillate  is  again  transferred
to  the  beaker,  30  c.c.  more  acid  are  added  to  the  flask,  and  the
whole  process  is  repeated ;  altogether  about  a  dozen  distilla-
tions, each  lasting  ten  minutes,  are  required  to  carry  over  the
last  traces  of  furfural.  In  order  to  ascertain  whether  the  dis-
tillate still  contains  furfural,  a  drop  of  the  liquid  is  placed  on  a

*  Neuberg  :  "  Ber.  deut.  chem.  Gesells.,"  1900,  35,  2243 ;  see  also  Mauren-
brecher  and  Tollens :   "  Ber.  deut.  chem.  Gesells.,"  1906,  39,  3578.
t  Krober  :  "J.  Landw.,"  igoo,  48,  357,  and  1901,  49,  7.
%  The  amount  chosen  should  be  sufficient  to  produce  from  '03  to  '03  gram  of
phloroglucide.
