446 
PREPARATION  OF   TANNIC  ACID, 
ing  dissolved  in  the  essence,  which  destroys  its  original  flavor. 
The  oil  of  lemons  presents  a  very  great  analogy  with  that  of  oil 
of  turpentine,  so  far  as  regards  its  transformations,  and  its  power 
of  rotating  a  ray  of  polarized  light.  Authorities  differ  as  regards 
this  latter  property.  Pereira  states  that  the  oil  of  turpentine  ob- 
tained by  distillation  with  water,  from  American  turpentine,  has  a 
molecular  power  of  right-handed  rotation,  while  the  French  oil  of 
turpentine  had  a  left-handed  rotation.  Oil  of  lemons  rotates  a  ray 
of  light  to  the  right,  but  in  France  a  distilled  oil  of  lemons,  sold  as 
scouring  drops  for  removing  spots  of  grease,  possesses  quite  the 
opposite  power  of  rotation,  and  has  lost  all  the  peculiar  flavor  of 
the  oil.  Oil  of  lemons  combines  with  hydrochloric  acid  to  form 
an  artificial  camphor,  just  in  the  same  manner  as  does  oil  of  tur- 
pentine, but  its  atom  is  only  one  half  that  of  the  oil  of  turpentine 
The  artificial  camphor  of  oil  of  lemons  is  represented  by  the  for- 
mula, C10  H8  H  CI;  the  artificial  camphor  of  oil  of  turpentine  by, 
C20  Hj65  H  CI. 
According  to  M.  Biot,  the  camphor  formed  by  the  oil  of  lemons 
does  not  exercise  any  action  on  polarized  light,  whilst  the  oil  of 
lemons  itself  rotates  a  ray  to  the  right.  The  camphor  from  oil  of 
turpentine,  on  the  contrary,  does  exercise  on  the  polarized  ray  the 
same  power  as  the  oil  possessed  while  in  its  isolated  state,  of  ro- 
tating to  the  left.  These  molecular  properties  establish  an  essen- 
tial difference  between  the  oils  of  turpentine  and  lemons,  and  may 
serve  to  detect  adulteration  and  fraud.  It  is  also  a  curious  fact, 
that  from  the  decomposition  of  these  artificial  camphors  by  lime, 
volatile  oils  may  be  obtained  by  distillation,  isomeric  with  the 
original  oils  from  which  the  camphors  were  formed  ;  but  in  neither 
case  has  the  new  product  any  action  on  polarized  light. 
In  conclusion,  I  would  recommend  that  this  oil,  as  well  as  all 
other  essential  oils,  be  kept  in  a  cool,  dark  place,  where  no  very 
great  changes  of  temperature  occur. — Annals  of  Pharm.  Feb.  1853. 
ON  THE  PREPARATION  OF  TANNIC  ACID. 
On  testing  the  method  prescribed  in  the  Prussian  Pharmacopoeia, 
for  the  preparation  of  tannic  acid,  Sandrock  finds  that  it  does  not 
fulfil  the  desired  object.  In  directing  that  water  should  be 
added  to  the  ether  employed,  the  authors  of  the  Pharmacopoeia 
