ON  TANNIC  ACID  IN  WOODY  PLANTS.  53 
This  liquor  was  tested  with  Soleil's  polarising  apparatus,  but 
there  was  no  sensible  change  in  the  color  of  the  doubly  rotating 
plate,  clearly  indicating  that  there  was  not  the  smallest  quantity 
of  sugar  or  of  gum  present.  To  be  still  more  certain,  I  decomposed 
the  acetate  of  lead  contained  in  this  solution  with  sulphuretted 
hydrogen,  and  after  filtering  it,  carefully  evaporated  the  clear 
liquor.  There  was  no  residue  left  after  the  evaporation,  although 
I  used  200  grammes  of  liquid. 
Thus  it  would  appear  that  tannin  does  not  contain  sugar  nor 
gum,  nor  any  other  similar  principle,  in  combination  with  the 
gallic  acid.  When,  under  the  influence  of  the  pectic  fermen- 
tation, or  of  sulphuric  acid,  tannin  is  transformed  into  gallic  acid, 
there  occurs  a  simple  molecular  change,  accompanied  by  hydration, 
just  as  cane  sugar  under  the  influence  of  yeast  is  transformed  into 
grape  sugar,  before  its  conversion  into  alcohol  and  carbonic  acid. 
It  remains  for  me  to  confirm  this  view  of  the  subject  by  a 
minute  analysis  of  all  the  tannates  and  gallates  which  can  be 
obtained  of  constant  composition. — London  Pharmaceutical  Jour- 
nal from  Journal  de  Pharmacie. 
ON  THE  OCCURRENCE  OF  TANNIC  ACIDS  IN  WOODY  PLANTS. 
AND  THEIR  CONNEXION  WITH  THE  FORMATION  OF  WOOD. 
By  Prof.  Pettenkofer. 
Some  years  since,  Pettenkofer  stated  that  wood  vinegar  con- 
tained pyrogallic  acid.  Further  investigations  have  shown,  that 
the  pyrogenous  acid  contained  in  wood  vinegar  does  not  behave 
exactly  like  pyrogallic  acid.  Pettenkofer  has  now  found  the 
means  of  isolating  the  acid  from  the  wood-vinegar. 
The  residue  of  the  distillation  of  wood-vinegar  is  treated  with 
a  concentrated  solution  of  chloride  of  sodium  or  of  some  other 
salt.  The  pyrogenous  acid  dissolves  in  this,  whilst  the  inter- 
mixed resinous  matters  remain.  The  acid  is  then  extracted  by 
ether,  which  leaves  it  almost  in  a  pure  state  on  evaporation. 
This  acid  is  obtained  not  only  by  the  dry  distillation  of  bark, 
but  also  by  that  of  wood;  and  the  quantity  of  acid  "is  not  di- 
minished even  when  the  wood,  before  distillation,  is  very  finely  di- 
vided and  treated  with  the  usual  solvents,  even  solution  of  potash. 
