Estimation  of  Alcohol. 
f  Am.  Jour.  Pharm. 
(   February,  1909. 
glycerol,  an  entirely  negligible  quantity.  One-half  of  one  of  these 
distillates  was  evaporated  on  the  water-bath  to  about  i  c.c.  and  the 
evaporation  continued  to  constant  weight  in  a  desiccator  over  sulph- 
uric add.  The  residue  weighed  0.0007  gramme,  equivalent  to  0.0014 
gramme  for  the  entire  distillate,  or  0.006  per  cent,  calculated  as 
glycerin.  Water  was  then  added  to  the  residue  from  the  last  dis- 
tillation (in  the  distilling  flask),  and  about  90  c.c.  distilled  off. 
After  diluting  to  100  c.c.  the  specific  gravity  was  1.0000096  at  ^  ; 
glycerin,  0.004  Per  cent-  Fifty  c.c.  of  this  distillate  gave  a  residue 
of  0.0013  gramme  or  0.0026  gramme  for  the  entire  sample;  equiva- 
lent to  0.0112  per  cent,  of  glycerin. 
Mixed  500  c.c  of  the  diluted  alcohol  and  250  c.c.  of  the  glycerin 
mixture  with  sufficient  water  to  make  1000  c.c.  after  allowing  for 
contraction.  By  calculation  this  mixture  contains  24.524  per  cent, 
of  alcohol  and  about  5.9  per  cent,  of  glycerin.  The  alcohol  was 
determined  in  each  of  two  100  c.c.  samples.  A:  specific  gravity, 
0.971671 ;  alcohol,  24.33  Per  cent. ;  loss,  0.194  per  cent.  B  :  specific 
gravity,  0.971 701 ;  alcohol,  24.30  per  cent. ;  loss,  0.224  per  cent. 
Mean  loss,  0.209  per  cent.  A  mean  alcoholic  loss  of  0.209  per  cent, 
in  this  determination  (in  which  glycerin  was  present),  compares 
favorably  with  a  mean  loss  of  0.26  per  cent,  of  alcohol  in  the  de- 
terminations in  a  preparation  containing  no  glycerin.  Evaporation 
of  50  c.c.  from  one  of  these  distillates  gave  no  weighable  residue. 
A  mixture  of  alcohol  and  water  was  assayed  for  alcohol  by  the 
usual  method,  50  c.c.  being  taken  for  the  test;  specific  gravity, 
0.96889 ;  alcohol,  26.95  per  cent.  Another  sample  of  50  c.c.  of  the 
same  mixture  was  taken,  10  per  cent,  of  glycerin  added,  and  the 
alcohol  determined  as  above :  specific  gravity,  0.96890 ;  alcohol, 
26.937  per  cent. ;  loss,  0.02  per  cent.  The'se  apparent  losses  could 
have  been  due  to  two  possible  causes :  ( 1 )  A  portion  of  the  glycerin 
may  have  been  volatilized,  thus  causing  an  increase  in  the  specific 
gravity  of  the  distillate,  or,  (2)  a  portion  of  the  alcohol  may  have 
escaped  by  leakage  through  the  joints  of  the  apparatus.  That  the 
first  theory  is  untenable  is  seen  by  the  fact  that  the  alcoholic  dis- 
tillates gave  no  weighable  residues  on  evaporation. 
From  the  foregoing,  it  is  reasonable  to  conclude  that  glycerin  does 
not  appreciably  affect  the  determination  of  alcohol. 
In  mixtures  of  glycerin  and  alcohol  only,  both  may  be  determined 
from  one  sample,  as  follows :  Determine  the  alcohol  in  the  usual 
way,  make  up  the  residue  in  the  distilling  flask  to  the  original  volume, 
