454       Chemistry  of  Oak,  Willow  and  Elm  Barks.  {^figSg*- 
ble  in  alcohol,  slightly  soluble  in  ether,  and  forms  an  imperfectly  clear 
solution  in  water.  In  its  behavior  to  litmus  paper,  metallic  salts,  and 
alkaloids,  it  is  completely  analogous  to  gallotannic  acid.  Dried  at  I  io°C, 
it  lost  8*48  percent,  of  water.  On  analysis,  it  gives  54*6 1  percent,  of 
carbon,  5*32  per  cent,  of  hydrogen,  and  40*07  per  cent,  of  oxygen, 
agreeing  approximately  with  Wagner's  formula,  C14H1608,  which 
requires  53*85  percent,  of  carbon,  and  5*13  per  cent,  of  hydrogen.  It 
contains  also  0*77  per  cent,  of  nitrogen  and  0*13  percent,  of  ash. 
Willow  Tannin  consists  of  a  brown-red  amorphous  body,  with  a 
slightly  astringent  taste  ;  easily  soluble  in  alcohol,  slightly  soluble  in 
ether,  and  forming  a  thick  solution  with  water.  With  ferric  salts  it 
gives  a  deep  black  color,  turned  violet-red  by  alkalis.  It  precipitates 
mercuric  nitrate  and  chloride,  and  zinc  and  copper  sulphates,  as  well  as 
albumin,  starch  and  alkaloids.  At  1200  the  willow  tannin  lost  IO'IO 
percent,  of  water,  and  on  analysis  gave  5 1  -13  percent,  of  carbon,  4*78 
per  cent,  of  hydrogen,  and  44*09  per  cent,  of  oxygen.  It  contains  also 
1*88  per  cent,  of  nitrogen  and  1*63  per  cent,  of  ash.  Another  speci- 
men, prepared  in  a  different  manner,  though  possessing  the  same  reac- 
tions as  the  last,  contained  51*26  percent,  of  carbon  and  5*99  per  cent, 
of  hydrogen,  besides  having  independently  044  per  cent.,  of  nitrogen 
and  1*42  per  cent,  of  ash. 
Elm  Tannin. — In  appearance  and  solubility  this  variety  resembles 
oak  tannin.  With  ferric  chloride,  it  gives  a  dirty-green  precipitate, 
turned  violet-red  by  sodium  hydrate.  With  ferrous  sulphate,  it  gives 
a  pure  green  precipitate.  It  precipitates  lead  and  copper  acetates,  and 
zinc  suplhate  after  some  time.  With  zinc  chloride,  mercuric  nitrate, 
calcium  acetate,  etc.,  it  gave  the  usual  reactions.  At  no°  elm  tannin 
loses  3*32  per  cent,  of  water,  and,  on  analysis,  gives  44*54  per  cent,  of 
carbon,  4*72  per  cent,  of  hydrogen,  and  50*74  per  cent,  of  oxygen, 
besides  containing  l"2l  per  cent,  of  ash. 
The  salts  of  these  three  tannin  acids  (quercitannic,  salitannic  and 
ulmotannic)  were  next  examined. 
Lead  Salts. — Quercitannate  of  lead  is  a  chocolate-brown,  amor- 
phous mass,  slightly  soluble  in  water,  insoluble  in  alcohol  or  ether.  On 
heating  it  to  no°,  it  lost  9*66  per  cent,  of  water;  and  on  analysis  it 
gave  22*85  per  cent,  of  carbon,  1*47  per  cent,  of  hydrogen,  9*14  per 
cent,  of  oxygen  and  66*54  per  cent,  of  lead  oxide.  The  salitannate 
of  lead  resembled  the  last  body,  and  on  drying  at  1200  lost  4*50  per 
