^54  Suggested  VS. P.  Tests  for  Glycerin.  {^j^im**' 
be  determined  with  greater  definiteness  from  tests  exactly  stated. 
Tests  involving  treating  glycerin  with  ammonia  and  silver  salts, 
or  with  ammoniacal  silver  salts,  and  requiring  heating  with  alkaline 
copper  solutions,  are  unreliable,  and  likely  to  give  erratic  results  in 
the  hands  of  different  analysts,  and  should  be  abandoned.  Such 
requirements  should  obtain  that  will  insure  a  quality  of  glycerin 
with  only  innocuous  limits  of  impurities,  and  such  as  is  contemplated 
by  the  Food  and  Drugs  Act,  and  the  necessary  tests  for  the  deter- 
mination of  the  purity  of  glycerin  should  be  set  forth  in  such 
language  that  there  can  be  no  erroneous  conclusions,  regardless 
of  the  measure  of  intelligence  of  the  analyst,  conceding  always, 
of  course,  that  the  analyst  must  necessarily  have  such  knowledge 
and  ability  in  chemistry  to  make  the  tests.  The  requirements  also 
should  be  such  as  will  avoid  any  possibility  of  advantage  to  any 
dishonest  refiner,  by  reason  of  tests  that  permit  of  any  controversy 
or  contention  as  to  the  meaning  thereof. 
With  such  purpose  in  view  it  is  suggested  that  taste  and  odor 
tests  be  eliminated,  since  two  different  individuals'  senses  of  taste 
or  smell  are  almost  invariably  widely  different,  one  chemist  some- 
times being  of  the  opinion  that  there  is  a  foreign  taste  or  smell, 
while  another  equally  careful  and  exacting  chemist  can  detect 
neither,  resulting  in  contention. 
Specifications  are  herewith  submitted  as  requirements  covering 
all  possible  impurities  to  be  found  in  chemically  pure  glycerin: 
Specific  gravity,  not  less  than  1.249  at  250  C.  (=95  per  cent, 
glycerin).  Factor  of  .00061  to  be  added  for  each  degree  of  tem- 
perature below  25 0  C,  between  15 0  and  25 0  C,  at  which  gravity 
is  determined.  The  gravity  to  be  ascertained  by  picnometer,  or 
by  means  of  an  accurate  plummet  (as  employed  with  a  Westphal 
specific  gravity  balance),  suspended  from  the  arm  of  an  analytical 
balance  sensitive  to  one-tenth  milligramme. 
Carbonaceous  residue,  including  mineral  and  carbonized  organic 
impurities,  not  to  exceed  .01  per  cent.  Test :  weigh  50  grammes 
of  glycerin  in  a  tared  platinum  dish,  heat  cautiously  until  it 
inflames  upon  direct  application  of  fire  (say  from  lighted  match), 
then  remove  the  source  of  heat  (preferably  Bunsen  burner),  and 
allow  the  glycerin  to  burn  away  in  a  place  free  from  draught; 
transfer  the  dish  to  a  desiccator,  and  weigh  when  cold. 
Ash,  including  chlorides,  not  to  exceed  .007  per  cent.  Test: 
incinerate  the  carbonaceous  residue  at  a  dull  red  heat  until  carbon 
