Am.  Jour.  Pharm. ) 
July,  1885.  J 
Commercial  Tannin. 
343 
the  precentage  of  tannic  acid  in  the  tannins,  and  with  tliat  view  I  pro- 
cured nine  samples  from  different  sources.  The  samples  are  those  of 
London,  Edinburgh,  and  German  manufacturers  in  almost  equal  pro- 
portions, and  may  therefore  be  taken  to  be  fairly  representative.  I 
may  remark  in  passing  that  a  number  of  so-called  makers  do  not  in 
reality  manufacture  or  extract  the  tannin,  but  simply  confine  them- 
selves to  ihe  punjication  of  the  German  product. 
It  may  be  of  advantage,  before  referring  to  their  composition,  to 
note  the  physical  characteristics  of  the  samples.  In  general  appearance 
they  vary  considerably,  some  being  crystalline  or  scaly,  Nos.  1  and  5 
especially  so,  while  others  are  almost  destitute  of  scales.  They  are  for 
the  most  part  of  a  light  yellow  oi  pale  straw  color,  one  only.  No.  1, 
being  of  a  perceptibly  darker  shade.  The  variation  in  weight  is  very 
remarkable,  some  of  the  samples  being  extremely  light  while  others 
are  comj)aratively  heavy.  The  specific  gravity  of  the  samples  was  not 
taken,  but  their  relative  weights  were  roughly  determined  ;  from  these 
it  will  be  seen  that  as  a  rule  the  weight  bears  a  striking  relation  to  the 
percentage  of  tannic  acid,  viz.,  the  lighter  the  tannin  the  higher  the 
proportion  of  tannic  aci-l  content. 
The  solubility  of  tannin  is  variously  stated,  the  range  being  from  1 
in  0*8  of  Avater  to  1  in  6.  I  have  not  attempted  more  than  an  approxi- 
mate determination  of  the  solubility  of  the  diflPerent  samples,  so  that 
the  figures  given  must  not  be  assumed  to  be  definite.  So  far  as  I  have 
gone,  the  solubility  seems  to  bear  no  relation  to  the  percentage  of 
tannic  acid. 
It  is  frequently  of  practical  value  to  know  the  time  required  for  a 
given  quantity  to  dissolve,  and  with  the  view  of  ascertaining  this,  10 
grains  of  each  sample  were  shaken  up  with  one  ounce  of  distilled  water 
at  60°  F.  No.  1  dissolved  in  half  a  minute,  5,  6,  and  8  in  two  minutes^ 
2  and  9  in  three  minutes,  while  3,  4,  and  7  were  only  partially  dis- 
solved at  the  expiration  of  fifteen  minutes.  The  residue  in  3  and  4 
dissolved  at  once  on  the  solutions  being  heated  to  80°  F.,  while  that  in 
No.  7  still  remained  undissolved.  The  aqueous  solutions  presented 
points  of  contrast  that  are  interesting.  Nos.  2,  5,  6,  and  8  were  per- 
fectly clear,  3  and  4  were  slightly  muddy,  1  and  9  still  more  so,  and  7 
most  of  all.  On  heating  the  muddy  solutions  to  80°  F.,  the  opacity 
almost  entirely  disappeared  from  3  and  4,  but  not  from  1,  7  and  9. 
The  insoluble  matter  in  No.  7  was  of  a  resinous  nature ;  the  propor- 
tion being  very  small  it  was  not  estimated. 
