n8  Assay  Processes  of  U.S. P.  IX.  {AnLMJaS1I^n1, 
of  menthol  being  156.16.  B  represents  the  weight  of  acetylized  oil 
used.  But  as  the  calculation  must  be  made  upon  the  basis  of  men- 
thol, the  difference  between  the  molecular  weights  of  menthyl  ace- 
tate and  menthol  must  be  subtracted  from  it  for  each  mil  of  KOH 
consumed. 
Menthyl  acetate  is  C10H19C2H3O2   M.W.  198.18 
Menthol  is  C10H19OH    M.  W.  156.16 
The  difference  between  the  molecular  weights  is   42.02 
In  the  saponification  of  the  ester  one  molecule  of  menthyl  acetate  re- 
quires one  molecule  of  KOH.  If  calculated  upon  the  basis  of  half- 
normal  alkali  2,000  mils  would  be  required.  Dividing  this  differ- 
ence of  molecular  weights,  42.02,  by  2,000  a  quotient  of  .021  is  ob- 
tained, and  this  is  the  coefficient  for  each  mil  half-normal  alkali 
consumed. 
Oil  of  rosemary  and  sandalwood  are  assayed  by  the  same 
method.  The  changes  in  calculation  are  A  X  7-7^7  for  the  former 
and  A  X  Il.n  for  the  latter.  The  ester  of  rosemary  is  bornyl  ace- 
tate, C10H17C2H3O2  (M.  W.  196.16),  of  which  not  less  than  2  per 
cent,  must  be  present.  The  alcohol  is  borneol,  C10H17OH  (M.  W. 
154.14),  of  which  the  oil  should  contain  not  less  than  10  per  cent, 
of  total  borneol. 
Oil  of  sandalwood  should  contain  not  less  than  90  per  cent,  of 
the  alcohols  calculated  as  santalol,  C15H25OH  (M.  W.  222.2). 
Two  of  the  volatile  oils,  caraway  and  cinnamon,  are  assayed 
by  the  sulphite  method,  depending  upon  the  property  that  one  of 
the  principles  is  soluble  in  sodium  sulphite  solution  and  the  other 
insoluble.  Oil  of  caraway.  10  mils  of  the  oil  are  placed  in  a 
cassia  flask,  and  50  mils  of  neutral  saturated  sodium  sulphite  solu- 
tion are  added.  The  mixture  is  heated  on  a  water  bath,  and  the 
flask  is  repeatedly  shaken,  and  the  mixture  neutralized  by  additions 
of  dilute  acetic  acid.  When  cool,  sufficient  solution  of  sodium  sul- 
phite is  added  to  raise  the  lower  limit  of  the  oil  within  the  graduated 
portion  of  the  flask.  The  decrease  in  volume  subtracted  from  the 
volume  originally  taken  will  give  the  value  of  carvone,  C10H14O, 
present;  which,  when  divided  by  the  volume  originally  taken,  gives 
per  cent,  by  volume  of  carvone.  Carvone  is  a  ketone,  isomeric  with 
carvacrol  and  thymol.  Carvacrol  and  thymol  are  phenols.  In  the 
former,  the  (OH)  is  in  the  ortho  position,  and  in  the  latter,  it  is  in 
the  meta  postion. 
