3i6 
Analysis  of  Ointments. 
(  Am.  Jour.  Pharm. 
I        July,  1910. 
edge  of  another  slide  to  distribute  it  in  a  thin  layer  over  the  surface. 
Examine  first  with  a  magnification  of  about  250  then  500  diameters. 
Repeat  this  after  drawing  slide  several  times  through  a  small  flame 
to  allow  fat  which  might  be  present  to  melt.  The  presence  of 
starch,  powdered  drugs,  crystalline  or  amorphous  bodies,  fatty  acid 
crystals,  etc.,  can  thus  be  readily  detected. 
Preliminary  Tests. — Submit  a  sample  of  the  ointment  in  a  test 
tube  for  about  half  an  hour  to  the  warmth  of  a  steam  bath.  Water 
and  glycerin  when  present  will  separate  from  fat.  Salts  an'd 
mineral  matter  may  settle  down  or  be  suspended  in  the  melted  fat, 
for  instance,  lead  carbonate,  zinc  oxide,  boric  acid,  etc. 
Determine  the  solubility  of  the  excipient  in  ether,  chloroform, 
benzin,  alcohol,  etc.  Any  water  present  must  be  removed  by 
drying  before  applying  the  solvent.  Starch,  powdered  drugs,  talcum 
and  others  can  be  so  separated  from  a  fat-base  and  weighed  after 
completely  removing  base  with  the  proper  solvent. 
Ointments  containing  fats  or  fatty  oils  will  give  a  greasy  stain 
on  paper  which  does  not  disappear  on  heating  or  exposure  to'  the  air 
(difference  from  ointments  having  starch  paste,  mucilage  of  traga- 
canth,  soap,  etc.,  as  basis). 
Reaction. — A  strongly  alkaline  reaction  may  be  due  to  sodium  or 
potassium  carbonate  (for  example  in  massage  cream  to  be  used 
for  reduction).  In  this  case  shake  a  sample  of  the  ointment  in  a 
test  tube  with  hot  diluted  hydrochloric  acid  to  see  if  there  is  effer- 
vescence. Zinc  carbonate  or  calcium  carbonate  are  frequently  found 
in  cosmetic  creams. 
Moisture  (water)  including  volatile  substances  (volatile  oils). 
An  accurately  weighed  sample  of  the  ointment,  one  to  two  grammes, 
is  heated  in  a  flat  platinum:  dish  at  a  temperature  of  105 0  until 
weight  is  approximately  constant,  weighing  at  half-hour  intervals. 
Too  long  continued  drying  must  be  avoided  as  fats  are  liable  to 
oxidize  with  increase  of  weight.  In  the  presence  of  a  considerable 
amount  of  water  it  is  recommended  to  mix  the  ointment  in  a  plati- 
num dish  with  a  weighed  portion  of  washed  and  freshly  ignited 
sea  sand.  Considerable  water  can  be  incorporated  with  a  fat- 
excipient  other  than  lanolin  and  eucerin  by  the  addition  of  borax, 
potassium  carbonate  or  alum. 
Ash.— This  is  preferably  done  quantitatively  in  order  to  save  a 
second  ignition  for  the  quantitative  analysis.  Two  to  three  grammes 
of  the  sample,  which  should  be  free  from  incorporated  water,  are 
