464 
Estimation  of  Glycerin  in  Fats. 
Am.  Jour.  Pharm. 
Sept.,  1887. 
ON  THE  ESTIMATION  OF  GLYCEKIN  IN  FATS.1 
By  Otto  Hehner. 
In  the  publication  of  the  principle  upon  which  the  method  to  be 
described  in  the  following  paper  is  based,  I  have  quite  recently  been 
forestalled  by  L.  Legler  [Analyst,  January  1887),  and  I,  therefore, 
cannot  lay  any  claim  to  originality.  But  as  I  operate  in  a  manner 
quite  different.froni  that  adopted  by  Legler — his  process  being  only 
applicable  to  somewhat  concentrated  glycerin  liquor,  whilst  I  am  en- 
abled to  determine  the  glycerin  in  even  the  most  dilute  solutions — I 
venture  to  lay  a  description  of  it,  and  of  results  obtained,  before  the 
members  of  the  Society.  A  portion  of  my  investigation  is,  further- 
more, of  general  importance,  and  concerns  all  methods  of  glycerin 
estimation,  since  it  treats  of  the  question  of  the  volatility  ot  glycerin 
with  aqueous  vapor. 
Glycerin  decomposes,  on  treatment  with  bichromate  of  potassium 
and  sulphuric  acid,  into  carbonic  acid  and  water.  Legler  weighs  the 
carbonic  acid,  or  rather  the  loss  of  carbonic  acid,  in  an  ordinary  car- 
bonic acid  apparatus.  Messrs.  Cross  and  Bevan  {Chemical  News, 
Vol.  56,  p.  2),  measure  the  volume  of  the  gas  evolved. 
It  is  evident  that  both  these  modifications  require  limited  bulks  of 
fluid,  and,  therefore,  exclude  the  estimation  of  glycerin  in  very  di- 
lute solutions,  such  as  are  obtained  in  the  analysis  of  fat — the  wash- 
ings, in  fact,  of  the  insoluble  fatty  acids. 
The  process  which  I  have  described  (Analyst,  XII,  February)  for 
the  estimation  of  methyl  in  the  presence  of  ethyl-alcohol,  and  which 
consists  in  the  measurement  of  the  quantity  of  bichromate  reduced, 
is,  as  I  hope  to  show,  particularly  suitable  for  the  analysis  of  such 
washings. 
One  part  of  glycerin  requires,  for  complete  oxidation,  7*486  parts 
of  potassium  bichromate. 
Solutions  required. — (1.)  Bichromate,  containing  in  each  litre  about 
80  grammes  of  bichromate  and  150  c.c.  of  strong  sulphuric  acid. 
The  exact  value  of  the  solution  should  be  ascertained  by  titration  with 
solutions  of  known  weights  of  iron  wire. 
2.  Ferrous  and  ammonia  sulphate  containing  about  120  grms.  per 
litre. 
/    3.  Bichromate  ten  times  more  dilute  than  the  above. 
xRead  at  the  meeting  of  Public  Analysts,  February  9th,  1887  ;  reprinted  from 
The  Analyst,  xii.  44. 
