A  jaSa?yfSm"}      Adulterations  of  Essential  Oils,  5 
The  optical  rotation  is  exceedingly  valuable,  frequently  being  the 
only  means  by  which  the  purity  of  an  oil  can  be  arrived  at,  and 
should  never  be  omitted. 
Fractional  distillation  is  usually  resorted  to  in  cases  of  admixture. 
The  congealing  -point  is  especially  useful  and  necessary  with  anise 
oils. 
QUANTITATIVE  ESTIMATION  OF  CONSTITUENTS. 
Before  an  oil  can  be  submitted  to  a  chemical  examination,  it  is 
necessary  to  know  at  least  its  chief  constituents,  and  then  the 
methods  must  be  so  adjusted  that  these  constituents  can  be  esti- 
mated quantitatively  with  a  considerable  degree  of  accuracy.  Such 
methods  have  been  elaborated  only  within  recent  times,  and  are 
based  on  well-known  organic  reactions. 
The  oldest  and  probably  the  most  useful  is  the  method  of 
ester  determination  or  saponification.  It  was  originally  applied  to 
essential  oils  as  we  now  apply  it  to  fixed  oils,  and  is  based  on  the 
fact  that  fixed  alkalies  resolve  the  esters  into  their  respective  alco- 
hols and  acids,  the  alkalies  combining  quantitatively  with  the  latter. 
Then,  knowing  the  ester  in  a  given  oil,  the  amount  can  readily  be 
calculated  by  the  quantity  of  alkali  consumed  by  a  given  weight  of 
oil.  The  linalyl  acetate  of  lavender  and  bergamot  oils  is  readily  es- 
timated by  this  process. 
Aldehydes. — In  the  case  of  aldehyde-bearing  oils,  as  cassia,  the 
property  of  sodium  bisulphite  forming  a  compound  soluble  in  water, 
containing  an  excess  of  sodium  bisulphite,  is  utilized.  This  process 
is  of  much  practical  value  with  oil  of  cassia,  and  the  oil  is  now 
generally  purchased  on  the  basis  of  aldehyde  content. 
Acetylization. — Many  of  the  oils  contain  alcohols  as  essential  con- 
stituents. These  can  mostly  be  estimated  by  converting  them  into 
acetic  esters,  by  means  of  acetic  anhydride,  removing  water-soluble 
products  by  washing  with  water,  then  dehydrating  the  residue  by 
means  of  fused  sodium  sulphate,  and  estimating  the  amount  of  acetyl 
group  contained  in  a  given  weight  of  the  acetylized  oil. 
PHENOL  DETERMINATION. 
It  is  the  custom  in  France  to  rectify  oil  of  thyme  with  consider- 
able quantities  of  turpentine  oil.  The  original  cause  of  this  pro- 
cedure is  probably  due  to  the  fact  that  the  consumer  requests  a 
colorless  oil,  and  oil  of  thyme  contains  a  goodly  per  cent,  of  phenol 
