476  Preparation  of  Glycerin.  (  Am>Sy^^9arm 
NOTE  ON  THE  PREPARATION  OF  GLYCERIN  BY 
FERMENTATION.1 
Karl  Schweizer  has  explained  his  experiments  which  led  to  a 
greatly  increased  yield  of  glycerin  during  the  fermentation  of 
sugar  by  yeast,  and  states  that  during  the  recent  war  certain  of  the 
belligerent  countries  have  prepared  their  glycerin  industrially  by 
this  method.  As  early  as  1857  Pasteur  found  that  glycerin  was 
formed  during  alcoholic  fermentation,  and  he  obtained  a  yield  of 
3.60  to  3.64  parts  for  100  parts  of  sugar  fermented.  Later  it  was 
found  by  Laborde  that  the  quantity  of  glycerin  formed  varies  with 
different  races  of  yeast,  and  obtained  as  much  as  7.75  Gm.  from  100 
Gm.  of  sugar.  It  has  been  found  also  that  the  amount  of  glycerin 
formed  ^s  greater  in  a  medium  rich  in  nutritive  matters,  and  less  in 
cases  where  the  conditions  are  less  favorable  for  the  growth  of  the 
yeast  plant.  It  was  evident  that  the  amounts  of  ethyl  alcohol  and 
glycerin  were  not  proportional. 
It  was  supposed  by  T.  Erlich  that  glycerin  could  be  formed 
from  certain  acid  amines,  as  is  the  case  with  amyl  and  other  higher 
alcohols,  and  thus  its  formation  was  attributed  to  the  fatty  matter 
that  is  found  in  little  droplets  in  the  yeast  cells,  but  it  was  demon- 
strated later  that  the  quantity  of  this  fat  was  too  small  to  explain 
the  formation. 
Oppenheim  proved  that  glycerin  can  be  formed  by  the  reduc- 
tion of  glycerin  aldehyde  and  of  dioxyacetone,  substances  that  are 
formed  during  alcoholic  fermentation,  and  various  hypotheses  were 
made  in  regard  to  the  intermediate  products  of  the  transformation 
of  sugar  into  alcohol.  It  appeared  plausible  to  the  author  that  the 
use  of  reducing  agents  in  the  fermenting  liquid  might  increase  the 
yield  of  glycerin,  and  accordingly  experiments  were  made,  both  in 
his  laboratory  and  upon  a  technical  scale.  The  greatest  difficulty 
was  to  find  a  race  of  yeast  that  would  withstand  the  conditions,  but 
this  was  found  in  a  commercial  pressed  yeast  made  from  molasses. 
Powdered  zinc  in  dilute  sulphuric  acid  solutions  did  not  give  satis- 
factory results,  and  attempts  with  acid  solutions  were  abandoned. 
The  reduction  in  solutions  as  nearly  neutral  as  possible  by  means 
of  sodium  sulphite  in  the  presence  of  powdered  chalk  was  studied 
1  Helvetica  Chemica  Acta,  2,  167.  Reprinted  from  Amer.  Jour,  of  Sci- 
ence, May,  1919. 
