40 
Determining  Pentosans. 
Am.  Jour.  Pharm. 
January,  1920. 
the  high  price  asked  for  it.  Our  purpose  in  this  short  investigation 
was  to  try  to  overcome  this  difficulty  by  modifying  the  phenylhy- 
drazine  method  so  as  to  make  it  shorter  and  at  the  same  time  obtain 
results  by  this  method  which  would  agree  with  the  provisional 
phloroglucinol  method. 
Recent  investigations  make  it  more  and  more  evident  that  many 
compounds  other  than  the  pentoses  and  pentosans  give  furfurol 
when  they  are  distilled  with  hydrochloric  or  sulphuric  acid,  and  hence 
neither  the  phloroglucinol  method  nor  any  other  method  of  de- 
termining the  furfurol  coming  from  such  a  distillation  will  enable 
one  to  say  definitely  that  the  original  substance  contained  a  certain 
per  cent,  of  pentosans. 
We  thought  it  should  be  possible  to  precipitate  the  furfurol 
with  phenylhydrazine  and  determine  the  excess  of  phenylhydrazine 
in  the  filtrate  by  the  use  of  some  compound  which  would  oxidize 
the  phenylhydrazine.  Tests  were  made  using  solutions  of  phenyl- 
hydrazine  sulphate  and  iodine,  potassium  dichromate,  ferric  sul- 
phate, sodium  hypobromite  and  Fehling's  solution.  With  the  iodine 
almost  theoretical  results  were  obtained  when  a  large  excess  of  it  was 
used.  The  amount  of  ferrous  salt  found  was  always  less  than  the 
theoretical.  No  better  results  were  obtained  with  the  other  oxidizing 
agents.  These  results  are  in  harmony  with  what  Chattaway^  found 
in  his  work  on  the  hydrazines.  R.  Adan^  found  that  the  reaction 
between  phenylhydrazine,  zinc  and  copper  sulphate  always  gave 
less  than  the  theoretical  amount  of  nitrogen.  He  stated  that  sec- 
ondary products  such  as  chlorophenylhydrazine  and  diazo  compounds 
were  formed  when  hydrochloric  acid  was  present.  B-  Bbler^  found 
that  a  quantitative  yield  of  nitrogen  was  obtained  in  the  reaction 
between  an  ammoniacal  solution  of  copper  sulphate  and  hydrazine. 
We  thought  that  this  reaction  might  be  quantitative  for  phenyl- 
hydrazine  also  if  no  chloride  or  other  halogen  ion  was  present  in 
the  solution  to  cause  the  side  reactions  found  by  Adan.  The  dis- 
tillation, was  therefore  made  using  sulphuric  instead  of  hydrochloric 
acid  and  using  sodium  sulphate  instead  of  sodium  chloride  to  lessen 
the  solubility  of  the  precipitate.^    In  the  distillation  the  volume  in 
^  /.  Cliem.  Soc,  91:  1323,  1907;  95:  1065,  1909. 
2  Bull.  soc.  chim.  Belg.,  21:  211,  1907;  abstracted  in  J.  Chem.  Soc,  [II]  91: 
657i  1907. 
3  Z.  anorg.  Chem.,  47:  371,  1905 ;  abstracted  in  /.  Chem.  Soc,  [II]  90: 53,  1906. 
*  Recommended  in  U.  S.  Department  of  Agriculture,  Bureau  of  Chemistry, 
Bulletin  49. 
