Am.  Jour.  Pharm. 
April,  1897. 
Estimation  of  Menthol. 
191 
C17H32O.C2H3O.C02K  +    KOH  =  C17H32(OH)C02K  +  KC2H302 
Acetyl  Potassium  Potassium  Potassium 
Ricinoleate  of  Potassium.  Hydroxide.  Ricinoleate.  Acetate. 
J.  Lewkowitsch1  has  studied  the  above  process  very  thoroughly, 
and  is  continuing  his  work  at  present. 
In  1894  F.  B.  Power2  and  C.  Kleber  proposed  an  analogous 
method  for  estimating  menthol  in  oil  of  peppermint.  The  method 
is  briefly  as  follows :  About  20  grammes  of  the  oil  are  mixed  with 
30  c.c.  of  normal  alcoholic  sodium  hydroxide,  in  a  flask  provided 
with  a  reflux  condenser  and  heated  to  boiling  for  one  hour.  The 
uncombined  alkali  is  estimated  by  means  of  normal  sulphuric  acid, 
using  phenolphthalein  as  indicator.  Each  cubic  centimeter  of  the 
standard  alkaline  solution  consumed  represents  0-156  gramme  of 
menthol  in  the  form  of  ethers. 
The  contents  of  the  above  flask  are  repeatedly  washed  with 
water,  to  remove  the  alcohol  present  and  the  oily  portion  boiled  one 
hour  with  an  equal  volume  of  acetic  anhydride  and  2  grammes  of 
fused  sodium  acetate  in  a  flask  provided  with  an  inverted  condenser, 
the  end  of  the  condenser  tube  being  so  ground  as  to  fit  accurately 
into  the  neck  of  the  flask.  On  cooling,  the  contents  of  the  flask 
are  washed  with  ample  water,  then  with  a  dilute  alkaline  solution, 
the  alkalinity  removed  by  washing  with  water  again,  and  the  oily 
portion  ultimately  dried  with  calcium  chloride  and  filtered.  From 
8  to  10  grammes  of  the  acetylized  oil  are  treated  as  above  for  esti- 
mating the  combined  menthol. 
From  the  data  obtained  by  the  above  procedure  the  total  per 
cent,  of  menthol,  free  and  in  the  form  of  ethers,  may  be  calculated 
by  the  following  formula  : 
p  =        a  X  iy6 
5 —  (a  —  0042) 
P  equals  total  menthol ;  5  equals  grammes  of  acetylated  oil  used  ;  a 
equals  the  number  of  cubic  centimeters  of  normal  sodium  hydroxide 
required  for  saponification ;  and  0042  is  a  constant  obtained  by 
hScp,  Proc.  Chem.  Society,  72  and  91;  J.  Soc.  Chem.  Ind.,  9,  660. 
1890,  J.  Soc.  Chem.  Ind.,  9,  846;  Chemical  Analysis  of  Oils,  Fats,  Waxes, 
etc.,  1895,  by  Benedikt  and  Lewkowitsch,  p.  129. 
2 1894.,  Pharm.  Rundschau,  i2»  157  ;  Circular  of  Information,  No.  3,  by 
Fritzsche  Brothers,  p.  12. 
