Am.  Jour.  Pharm. 
March,  19 17 
}     Assay  Processes  of  US.P.  IX. 
117 
heated  solution  ammonia  water  is  added  until  precipitation  is  com- 
plete. After  washing  with  ammonium  nitrate  solution,  it  is  dried 
and  gently  ignited,  and  weighed  as  urano-uranic  oxide,  U3Os. 
The  methods  of  ascertaining  the  purities  of  the  volatile  oils  of 
the  U.  S.  P.,  other  than  methods  for  determining  their  physical 
constants,  such  as  polariscopic,  refractometric  and  gravity  methods, 
may  be  divided  into  several  groups :  Saponification,  for  the  deter- 
mination of  esters  and  phenols ;  acetylization,  for  determining  the 
alcohols ;  treatment  with  phenylhydrazine,  for  aldehydes ;  and  solu- 
tion in  sodium  sulphite. 
With  oil  of  peppermint,  two  distinct  assays  are  carried  out. 
First,  for  the  amount  of  ester,  and  secondly,  for  the  menthol.  The 
ester  of  oil  of  peppermint  is  menthyl  acetate,  C10H19C2H3O2,  of 
which  not  less  than  five  per  cent,  should  be  present.  The  assay  is 
carried  out  as  follows:  10  mils  of  the  oil,  the  exact  weight  of  which 
has  been  found,  are  treated  with  25  mils  of  half-normal  alcoholic 
KOH,  and  refluxed  for  one  hour.  After  cooling,  the  excess  of  al- 
kali is  titrated  with  n/2  sulphuric  acid,  and  the  number  of  mils  of 
alkali  used  multiplied  by  9.909,  and  divided  by  the  weight  of  oil 
taken,  gives  the  percentage  of  ester.  For  menthol:  The  official  re- 
quirements are  that  it  should  contain  50  per  cent,  total  menthol 
free  and  as  ester.  10  mils  of  the  oil  are  introduced  into  an  acetyli- 
zation flask,  to  which  are  added  10  mils  of  acetic  anhydride  and 
about  1  Gm.  anhydrous  sodium  acetate.  This  is  heated  for  one 
hour,  allowed  to  cool,  and  the  acetylized  oil  washed  with  water 
and  solution  sodium  carbonate,  until  the  washing  is  slightly  alkaline 
tophenolphthalein.  The  oil  is  then  dried  by  adding  calcium  chloride, 
filtered,  and  5  mils  of  it,  after  weighing,  are  placed  in  a  flask,  50 
mils  of  half-normal  alkali  added,  and  refluxed  one  hour.  After 
cooling,  the  residual  alkali  is  titrated  with  half-normal  sulphuric 
acid,  and  from  the  following  formula  the  percentage  of  menthol  is 
calculated. 
A  represents  the  number  of  mils  half-normal  alkali  used  in  the 
saponification.  7.808  is  100  times  the  amount  of  menthol  corre- 
sponding to  each  mil  of  half-normal  KOH,  the  molecular  weight 
Volatile  Oils. 
Percentage  of  menthol  - 
A  X  7.808 
B  -  (AX  .021)  ' 
