484 
New  Test  for  Glycerin. 
Am.  Jour.  Pharm. 
Oct.,  1878. 
must  be  neutral  or  faintly  alkaline.  Erythrite,  and  apparantly  glycol, 
also  give  the  same  green  flame,  but  could,  hardly  occur  so  as  to  be  mis- 
taken for  glycerin.  The  same  may  be  said  of  copper  salts  and  certain 
other  substances,  which  of  themselves  might  impart  a  green  color  to 
flame.  Other  substances,  such  as  sugars,  fats,  etc.,  were  tried,  but  all 
failed  to  give  this  test.  It  appears,  then,  in  the  absence  of  erythrite, 
and  probably  glycol,  to  be  a  property  fairly  characteristic  of  glycerin. 
The  test  is  applied  as  follows :  The  aqueous  solution  to  be 
examined  is  first  made  slightly  alkaline  with  dilute  soda-solution,  and  a 
borax  bead  is  dipped  into  it.  The  bead  is  allowed  to  rest  for  a  minute 
or  so  to  allow  solution  to  take  place  on  its  surface.  Then  it  is  held  in 
the  Bunsen  flame  in  the  usual  way.  Another  method,  and  this  we  find 
more  delicate,  is  to  place  a  little  powdered  borax  on- a  watch  glass,  and 
pour  on  to  it  some  of  the  solution  made  faintly  alkaline.  Stir  with  a 
glass  rod  (the  mixture  becomes  acid  of  course),  and  by  means  of  a 
looped  platinum  wire  introduce  some  of  the  mixture  into  the  flame. 
In  either  case  the  deep  green  color  appears  more  or  less  distinctly  if 
glycerin  be  present  in  sufficient  quantity. 
The  following  experiments  were  made  with  the  view  of  determin- 
ing the  extent  to  which  the  test  could  be  applied  to  the  detection  of 
glycerin  in  various  solutions.     The  percentages  are  by  volume : 
Glycerin  in  Water. — The  solutions  were  made  faintly  alkaline.  A 
20  per  cent,  solution  gave  the  color  very  decidedly.  Solutions  con- 
taining 15,  10  and  5  percentages  gave  the  color  distinctly.  i\  per 
cent,  gave  a  faint  color,  and  the  limit  seemed  to  be  reached  in  the  case 
of  a  1  per  cent,  solution,  which  gave  scarcely  any  color. 
Glycerin  in  Beer. — The  solutions  were  made  faintly  alkaline.  25 
and  20  per  cent,  solutions  gave  the  color  decidedly.  A  10  per  cent, 
solution  gave  it  distinctly,  but  in  the  case  of  a  5  per  cent,  solution  it 
could  scarcely  be  seen.  It  was  evident  from  these  experiments  that, 
in  order  to  detect  less  than  10  per  cent,  in  beer,  the  solution  of  glycerin 
would  have  to  be  concentrated,  and  some  of  the  foreign  matter 
removed.  To  try  this  we  prepared  two  solutions  of  glycerin,  one  con- 
taining 5  per  cent,  and  the  other  1  per  cent.  Both  were  treated  in  the 
same  manner.  50  cc.  were  evaporated  to  dryness  over  a  water-bath, 
and  the  residue  was  treated  with  50  cc.  of  absolute  alcohol.  Solution 
of  the  glycerin  in  the  alcohol  was  insured  by  well  stirring  the  mixture 
and  heating  to  boiling.    The  dish  containing  the  mixture  was  then  set 
