f 
110      ON  TESTING  GLYCERIN  FOR  SUGAR  AND  GLUCOSE. 
covery,  there  need  be  no  better  test  used,  pure  glycerin  not  re- 
ducing the  cupric  oxide. 
Mr.  Pope  appears  to  have  been  deceived  by  the  deep  blue 
color  which  the  mixture  acquires  after  the  contact  of  the  alkali. 
This  coloration  is  a  quality  of  glycerin  due  to  its  solvent  power 
on  the  cupric  oxide.  According  to  A.  Vogel  (Gmelin,  vol.  ix. 
490),  cupric  sulphate  mixed  with  glycerin  forms  a  clear  azure 
blue  mixture,  with  an  excess  of  potassa."  "Where  the  potassa 
is  in  smaller  quantity  a  precipitate  occurs,  but  this  is  soluble  by 
heat  and  a  further  addition  of  potassa ;  the  resulting  blue  solu- 
tion decomposes  below  212°,  depositing  a  flaky  precipitate." 
In  speaking  of  Vienna-  glycerin  Mr.  Pope  says,  "  however, 
upon  boiling  I  failed  to  get  the  precipitate  of  suboxide  of  cop- 
per," an  admission  at  once  clearing  the  sample  tested  from  the 
suspicion  of  glucose. 
As  cane  sugar  syrup  may  be  used  as  an  adulterant,  its  presence 
may  most  satisfactorily  be  detected  by  diluting  a  little  of  the  sus- 
pected glycerin  with  three  parts  of  water,  adding  a  few  grains  of 
tartaric  acid,  and  boiling  a  few  moments.  Then  add  the  solution 
of  sulphate  of  copper,  followed  by  the  potassa,  when  the  reddish 
suboxide  will  at  once  appear  if  cane  sugar  had  been  present,  the 
tartaric  acid  having  changed  the  cane  sugar  into  glucose. 
The  editor  of  the  Circular,  in  commenting  on  Mr.  Pope's 
remarks,  among  other  things  observes,  "  Another  method  of  de- 
tecting sugar  in  glycerin  is  by  means  of  chloroform,  in  which  gly- 
cerin dissolves  readily  whilst  sugar  is  quite  insoluble.  The 
liquid  [glycerin]  is  first  heated  to  drive  off  the  water  it  contains, 
then  mixed  with  chloroform.  The  whole  is  then  poured  on  a 
tared  filter  and  repeatedly  washed  with  chloroform,  after  which 
the  filter  and  its  contents  are  dried  at  212°  F.,  and  weighed. 
By  reference  to  the  U.  S.  Dispensatory,  12th  Edit.  p.  420, 
the  same  idea  is  suggested,  credited  to  the  Chemical  News  (1863, 
vol.  viii.  p.  227).  This  method  is  defective  from  the  fact  that 
commercial  glycerin  is  insoluble  in  chloroform,  and  consequently 
sugar  may  be  present  without  being  detected  by  this  means. 
We  have  tried  samples  of  four  different  manufacturers,  and  all 
are  equally  insoluble  in  chloroform.  Singularly  enough  the 
most  recent  works  on  chemistry  and  pharmacy  do  not  allude  to 
