Amj^fi£oam'}  Suggest^  V.S.P,  Tests  for  Glycerin.  255 
is  entirely  burned  off;  then  transfer  to  a  desiccator,  and  weigh 
when  cold. 
Chlorides,  not  to  exceed  .001  per  cent.,  figured  as  NaCl.  Test : 
put  the  ash  in  100  c.c.  distilled  water,  add  2  or  3  drops  of  a  cold, 
saturated  solution  of  neutral  chromate  of  potassium  (K2Cr04)  as 
indicator;  then  run  in,  from  accurately  calibrated  burette,  'N/106 
silver  nitrate  volumetric  solution  till  tinge  of  permanent  red  color 
appears;  the  c.c.  of  N/100  silver  nitrate  volumetric  solution  used, 
multiplied  by  .0005806  for  each  c.c,  and  then  by  2,  giving  the 
percentage  of  chlorine  as  sodium  chloride. 
Total  acid  equivalent,  in  terms  of  NaOH,  not  to  exceed  .02  per 
cent.  Test :  weigh  100  grammes  of  the  glycerin,  and  dissolve  in 
100  c.c.  of  distilled  water.  Use  phenolphthalein  solution  as  in- 
dicator. Run  in  10  c.c.  of  N/10  NaOH  solution  (3.976  grammes 
of  NaOH  to  1  litre)  from  a  burette,  heat  to  boiling  over  Bunsen 
burner,  and  continue  boiling  for  three  or  four  minutes,  then  titrate 
with  N/10  H2S04  solution  (4.8675  grammes  per  litre)  run  in 
from  a  burette,  until  pink  color  just  disappears.  The  NaOH 
solution  used,  less  the  H2S04  solution  used,  must  not  exceed  6  c.c. 
to  neutralize. 
Arsenic  not  to  exceed  1  part  in  100,000;  to  be  determined  by 
the  Gutzeit  test,  and  5  c.c.  of  a  i-in-10  aqueous  solution  of  the 
glycerin  placed  in  a  narrow-necked  flask  with  2  grammes  of  zinc, 
20  c.c.  of  hydrochloric  acid  (22.5  c.c.  concentrated  and  77.5  c.c. 
water).  The  flask  is  closed  by  a  filter  paper  saturated  with  alcoholic 
solution  of  mercuric  chloride,  and  dried.  The  neck  of  the  flask 
contains  a  roll  of  cheese  cloth  impregnated  with  10  per  cent, 
lead  acetate,  to  prevent  any  hydrogen  sulphide  from  reaching  the 
sensitive  paper.  The  flask,  60-75  c-c->  should  have  a  narrow  neck, 
and  the  circle  of  paper  exposed  should  be  about  1  cm.  in  diameter. 
The  action  is  allowed  to  continue  until  the  greater  part  of  the 
zinc  is  dissolved,  and  at  that  time  the  paper  should  not  be  stained 
a  distinct  yellow  or  orange. 
Silver  nitrate  test:  An  aqueous  solution  (2  c.c.  of  glycerin  to  10 
c.c.  of  distilled  water),  with  5  c.c.  of  N/10  silver  nitrate  solution; 
the  mixture  shaken  and  placed  in  a  dark  place  for  10  minutes  may 
assume  a  slight  pink  or  gray  tinge,  but  must  not  turn  red  nor 
black,  nor  give  a  precipitate  (limit  of  chlorides  and  impurities 
having  reducing  properties). 
Glycerin  conforming  to  the  above  tests  will  insure  such  purity 
