322 
Analysis  of  Ointments. 
(  Am.  Jour.  Pharm. 
(       July,  1910. 
acid  will  give  the  reaction  with  turmeric  paper  when  shaken  out  with 
hot  water;  borax  will  give  the  test  on  setting  free  the  boric  acid, 
using  acidulated  water  for  extraction. 
Quantitative  Analysis. — Metals  and  Their  Salts. — A  simple 
and  sufficiently  accurate  method  to  estimate  certain  metallic  com- 
pounds, insoluble  in  fat-solvents,  such  as  zinc  oxide,  carbonates  of 
zinc,  lead,  calcium,  and  bismuth  subnitrate  when  mixed  with  a  fat 
excipient  and  no  other  substances  also  insoluble  in  the  solvent  are 
present,  is  as  follows :  A  thoroughly  dried  and  weighed  sample  of 
the  ointment  is  mixed  in  a  beaker  with  the  proper  solvent  (see  pre- 
liminary tests),  the  mixture  transferred  to  a  dried  and  weighed 
filter  and  the  latter  with  the  remaining  substance  washed  with  the 
solvent  until  all  fat  is  removed.  The  filter  with  contents  is  allowed 
to  dry  at  100  to  105  °  C.  until  its  weight  remains  constant.  In  cal- 
culating the  percentage  of  the  material  thus  obtained,  the  loss  on  dry- 
ing the  ointment  must  of  course  be  taken  in  consideration. 
For  method  of  estimating  metallic  mercury  in  mercurial  ointment 
see  U.S.P. 
A  procedure  for  the  estimation  of  metals  in  organic  substances 
has  been  given  by  Rothe.6  It  is  based  on  the  observation  that 
organic  compounds  when  digested  for  a  sufficient  time  with  a  mix- 
ture of  fuming  nitric  acid  and  concentrated  sulphuric  acid,  and 
subsequent  heating  until  vapors  of  sulphuric  acid  escape,  are  decom- 
posed on  further  heating  with  fuming  nitric  acid  into  carbon  dioxide 
and  water.  To  the  material,  which  should  be  free  from  water,  is 
added  in  a  flask  10  to  15  c.c.  fuming  nitric  acid  and  2  c.c.  concen- 
trated sulphuric  acid  for  each  gramme  taken  and  the  flask  heated  on 
a  sand  bath  until  a  continuous  generation  of  gas  takes  place,  avoiding 
too  high  a  temperature.  Later  on  the  temperature  of  the  sand  bath 
is  increased  to  drive  off  the  nitric  acid  and  cause  the  sulphuric  acid 
to  develop  vapors.  To  this  end  the  flask  is  heated  over  the  free 
flame,  after  the  nitric  acid  has  escaped,  until  the  sulphuric  acid  boils 
briskly.  After  allowing  to  cool,  5  to  10  c.c.  fuming  nitric  acid 
are  added  and  the  flask  heated  again  on  the  sand  bath  to  slight  boil- 
ing until  the  liquid  turns  light,  which  will  require  from  one- 
quarter  to  one-half  hour.  Finally  the  flask  is  heated  once  more  over 
the  free  flame  to  a  brisk  boiling  until  heavy  vapors  of  sulphuric  acid 
are  given  off.  If  the  liquid  assumes  a  brown  color  the  organic 
matter  is  not  completely  destroyed  and  the  operation  must  be  re- 
peated by  the  addition  of  another  5  c.c.  of  fuming  nitric  acid  until 
