50 
ON  THE  COMPOSITION  OF  TANNIC  ACID. 
then  evaporated  in  vacuo;  the  residue  was  analysed  after  being 
dried  at  258°  F.  Ten  analyses  made  with  oxide  of  copper  in  a 
current  of  oxygen  gas  upon  substances  obtained  at  seven  different 
preparations,  gave  results  leading  to  the  formula  C54  II22  O34, 
I.       II.       III.       IV.        V.       VL      VII.     VIII.     IX.       X.  Calculated. 
G  525  52  2  52-2  52-2  52-2  52-3  52-1  52-2  52-3  52-3  54=52-4 
H  38  3-8  3-7  3-7  3  6  3-D  3-8  3  6  3»7  3-5  22=  3  6 
0         —__—_-_„____„_  34=44-0 
According  to  this  formula,  the  resolution  of  tannic  acid  into 
gallic  acid  and  glucose  may  be  represented  by  the  following 
equation 
G5i  H22  O34  -f  8HO  =3  (CM  H°  Ow  +  C12  H10  O10 
This  equation  is  confirmed  by  the  quantities  of  the  two  compounds 
obtained  by  the  decomposition  of  tannic  acid.    The  former  was 
found  to  be  87  per  cent*  (maximum)  by  Wetherill ;  of  glucose  I 
have  obtained  as  much  as  22  per  cent. 
The  quantity  of  water  which  may  be  displaced  by  metallic 
oxide  in  the  molecule  C54  H22  O34  I  have  determined  directly  by 
digesting  tannic  acid  with  oxide  of  lead,  and  the  analysis  of  the 
neutral  and  basic  salts.  By  the  former  method  I  found  that  the 
acid  loses  4-4  per  cent.,  or  3  equivs,  of  water,  which  is  confirmed 
by  the  analysis  of  the  salts  of  lead  prepared  by  precipitation,  in 
which  the  composition  of  the  anhydrous  acid  is  represented  by 
the  formula  C54  H19  O31,  differing  by  3  equivs.  of  water  from  the 
formula  C54  H22  O14.  The  precipitates  obtained  by  tannic  acid 
and  acetate  of  lead  contain  from  3  to  10  equivs.  of  oxide  of  lead? 
in  proportion  to  C54.  The  analysis  of  tan-nates  made  by  Pelouze7 
Liebig,  Berzelius,  Mulder  and  Bochner,  agree  with  the  new 
formula  of  tannic  acid,  if  we  suppose  that  some  salts  do  not  lose 
all  their  water  at  212°  F.,  or  that  they  were  not  completely 
dried. 
According  to  Berzelius,  tannic  acid  combines  with  sulphuric 
or  muriatic  acid,  and,  when  these  acids  are  added  to  a  solution 
of  tannic  acid  in  water.  In  these  cases  precipitates  are  obtained 
which  are  dissolved  at  the  commencement,  until  the  fluid  contains 
an  excess  of  sulphuric  or  muriatic  acid.  These  compounds  are 
distinguished  from  the  conjugate  acids,  as  the  mineral  acid  can 
be  separated  therefrom  by  salts  of  baryta  or  silver.  The  analysis 
©f  these  precipitates  shows  that  they  are  nothing  but  tannic  acid 
