1 
26  ON  TANNATE  OF  ALUMINA. 
ounce  of  the  tannic  acid  solution  until  it  is  saturated,  and  an 
equal  measure  of  the  solution  of  alum  is  added,  an  immediate 
bulky  gelatinous  precipitate  occurs,  similar  in  appearance  to  the 
magma  in  No.  1.  When  washed  and  dried  it  weighed  13  grains. 
The  washings  had  a  slight  astringent  taste,  and  afforded  a  slight 
inky  blue  precipitate  with  ter-chloride  of  iron. 
4th.  As  tannic  acid  is  considered  by  Liebig  to  be  tribasic,  three 
parts  of  solution  of  alum  was  added  to  one  of  solution  of  tannic 
acid,  with  sufficient  excess  of  ammonia  to  liberate  all  the  alumina. 
On  filtering  out  the  precipitate,  the  clear  liquid  yielded  no  pre- 
cipitate with  ammonia,  but  was  precipitated  blueish  black  by  ter- 
chloride  of  iron  ;  showing  that  in  the  presence  of  enough  alumina 
to  form  a  tribasic  salt,  a  part  of  the  tannic  acid  remains  in  solu- 
tion probably  as  tannate  of  ammonia. 
5th.  The  liquid  filtered  from  No.  3,  with  the  washings,  was 
evaporated  to  a  small  bulk,  and  on  standing,  dirty  yellowish  colo- 
red crystals  in  small  quantity  were  deposited.  The  mother  liquid 
poured  off  and  evaporated  gave  other  mamillary  crystals  admixed 
with  dark  matter.  The  first  crystals  had  the  well  known  trian- 
gular facets  of  alum,  and  when  tested  by  solution  in  hot  water, 
yielded  a  blueish-black  precipitate  with  ter-chloride  of  iron. 
When  powdered  and  boiled  in  repeated  portions  of  alcohol,  nearly 
all  the  color  is  removed,  and  they  give  but  a  trace  of  color  with 
the  ter-chloride,  whilst  the  alcohol  when  evaporated  yielded  a 
yellowish,  non-crystalline  residue,  which  reacted  as  tannic  acid 
with  the  ter-salts  of  iron,  and  was  not  precipitated  by  an  excess 
of  ammonia.  The  crystals,  after  treatment  by  alcohol,  yielded, 
when  dissolved  in  water,  a  white  insoluble  precipitate  with  chlo- 
ride of  barium,  and  a  gelatinous  precipitate  with  ammonia  and 
were  alum.  The  residue  from  the  mother  liquid  contained  sul- 
phate of  ammonia,  tannin  and  some  undecomposed  alum. 
From  these  results  it  appears  that  tannate  of  alumina  formed 
by  direct  combination,  is  an  amorphous  salt,  nearly  insoluble  in 
water.  That  the  same  salt  is  precipitated  from  alum  on  the 
addition  of  tannate  of  ammonia,  and,  finally,  that  it  is  probable 
that  the  tannate  of  alumina  of  Mr.  Harrison  is  a  mixture  of 
tannic  acid  and  alum,  derived  either  from  the  evaporation  of  a 
mixture  of  alum  and  tannic  acid ;  or,  from  the  washings  of  tan- 
nate of  alumina,  as  treated  in  No.  5. 
