326 
Analysis  of  Ointments. 
j  Am.  Jour.  Pharm. 
\      July,  1910. 
— casein,  alkaloids,  etc.,  or  to  show  the  absence  of  such  bodies.  A 
small  nitrogen  content,  due  to  impurities  in  fats,  oils  or  waxes,  might, 
however,  be  met  with. 
Melting  Point. — At  least  24  hours  should  have  elapsed  since  the 
last  melting,  as  melted  fats  require  a  certain  time  to  acquire  their 
normal  melting  point.  Products  obtained  by  melting  together  bees- 
wax, paraffin,  stearic  acid,  etc.,  have  a  melting  point  lower  than  the 
mean  of  the;r  constituents.13  The  presence  of  an  appreciable  amount 
of  carnauba  wax  (melts  at  84  to  86°  C.)  or  rosin  (90  to  1300  C.) 
in  a  fat  base  increases  the  melting  point.  The  sample  must  of 
course  be  free  from  water,  salts,  mineral  matter,  glycerin,  etc. 
Ash. — See  under  preliminary  tests. 
Remarks. — As  a  general  rule  water  or  alcohol  soluble  constituents 
are  extracted  by  treating  the  sample  with  the  hot  solvent,  concen- 
trating the  aqueous  liquid  or  evaporating  the  alcohol,  and  testing 
in  the  usual  way  or  identifying  the  residue  from,  its  physical  charac- 
ter. The  water  and  alcohol  insoluble  constituents  are  separated 
from  a  fat  basis  by  dissolving  out  the  fat  with  ether  or  chloroform, 
filtering  off  the  solution  and  identifying  the  residue  on  filter  either 
chemically  or  microscopically.  In  the  presence  of  water  soluble 
and  water  insoluble  substances,  for  example,  boric  acid  and  zinc 
oxide,  the  former  are  removed  as  before;  the  remaining  fat  contain- 
ing the  water  insoluble  substance  must  be  thoroughly  dried  before 
dissolving  fat  in  solvent.  Two  water  insoluble  constituents  of 
an  ointment,  for  example,  starch  and  zinc  oxide,  or  starch  and 
talcum,  may  be  separated  from  each  other  after  removing  fat  by 
using  the  proper  solvent  of  one,  viz.,  diluted  acid  for  zinc  oxide 
or  incinerating  starch,  which  will  leave  the  talcum  behind. 
Volatile  substances  as  volatile  oils,  carbolic  acid,  etc.,  can  be  sepa- 
rated by  distillation  with  live  steam  and  their  identification  thus 
made  easier.  If  a  certain  known  odor  of  a  volatile  oil  can  not  be 
identified  by  its  name,  the  following  method  has  been  found  practical 
but  not  very  scientific.  On  looking  over  the  index  of  the  volatile 
oils  in  the  dispensatory  or  other  suitable  pharmaceutical  manual, 
one  might  strike  suddenly  the  name  of  the  oil  in  question  or  might 
be  able  to  select  a  few  for  comparison  with  the  original. 
The  amount  of  fat  basis  in  an  ointment  can  be  estimated  by 
dissolving  a  weighed  sample,  which  must  be  free  from  water,  in 
chloroform,  making  up  to  a  certain  volume  and  evaporating  an  ali- 
