Am.  Jour.  Pharm.  ) 
January,  1920.  j 
Determining  Pentosans. 
41 
the  flask  was  kept  practically  constant  by  adding  water  as  the  dis- 
tillation proceeded. 
After  the  addition  of  the  phenylhydrazine  to  an  aliquot  of  the 
distillate  the  solution  was  stirred  for  the  required  time  by  bubbling 
carbon  dioxide  into  it.  An  aliquot  (50  Cc.)  of  the  filtrate  from  the 
hydrazone  was  put  by  means  of  a  dropping  funnel  into  a  250  Cc. 
Fresenius  nitrogen  bulb/  which  had  been  previously  filled  with  a 
10  per  cent,  solution  of  ammoniacal  copper  sulphate  and  heated  to 
expel  the  air.  A  100  Cc.  burette  was  connected  to  the  tube  of  the 
Fresenius  bulb  and  a  glass  tube  provided  with  a  stopcock  connected 
the  neck  of  the  bulb  with  a  Schiff's  nitrometer  containing  sulphuric 
acid.  The  aliquot  of  the  filtrate  was  brought  into  the  bulb  through 
the  dropping  funnel  by  closing  the  cock  leading  to  the  nitrometer 
and  lowering  the  burette.  The  bulb  was  then  heated  so  as  to  keep 
the  reaction  mixture  near  the  boiling  point  until  the  reaction  was 
complete.  .  . 
Results  obtained,  using  the  above  method  to  determine  the  pen- 
tosans in  three  samples  of  grain  sorghum  which  were  cut  at  different 
stages  of  growth,  are  given  in  the  table  below.  Results  obtained  by 
Mr.  Freidemann  of  this  laboratory  using  the  same  samples  and  the 
phloroglucinol  method  are  given  for  comparison.  Neither  Mr. 
Freidemann  nor  Mr.  Menaul  knew  what  results  the  other  had  ob- 
tained until  the  work  had  been  finished. 
Table  Showing  Weights  of  Pentosans  in  One  Gram  of  Sorghum. 
Other  determinations  showed  that  the  addition  of  sodium  sul- 
phate to  the  distillate  with  the  phenylhydrazine  was  not  necessary. 
The  same  volume  of  nitrogen  was  obtained  by  taking  two  parts 
of  the  distillate  to  one  of  which  sodium  sulphate  had  been  added 
and  not  to  the  other. 
The  time  required  to  make  a  determination  of  the  excess  of 
phenylhydrazine  in  the  filtrate  is  about  20  min.  This  method  then 
makes  it  possible  to  use  a  much  cheaper  substance  than  phloroglu- 
No. 
Phloroglucinol 
Method. 
Gram. 
Phenylhydrazine 
Method. 
Gram. 
I.. 
II. 
Ill 
o. 1790 
o- 1523 
o. 2149 
0.1788 
o.  1526 
o. 2150 
5  See  catalogue  of  Central  Scientific  Company,  p.  371. 
