NITRATE  OF  SILVER  AND  TANNIC  ACID  IN  PILLS. 
413 
is  mixed  with  powdered  sugar  and  moderately  heated,  it  gives  off 
bubbles  of  hydriodic  acid,  becoming  darker  in  color,  reacting 
strongly  with  starch,  and  ultimately  becoming  completely  black, 
with  abundance  of  free  iodine. 
The  precise  action  of  sugar  with  reference  to  those  compounds 
that  have  been  named,  is  still  obscure.  Klauer  considers  that  a 
regular  compound  is  formed  in  the  case  of  carbonate  of  iron,  but 
the  subject  of  this  notice  is  an  instance  where  the  action  of  sugar 
i%s  not  confined  to  salts  of  iron. 
In  conclusion,  it  is  very  probable  that  the  protective  agency 
of  sugar,  is  exercised  over  many  other  decomposable  substances 
that  have  not  been  examined  as  to  this  property ;  and  if  it  be  so, 
it  must  become  of  corresponding  importance  as  a  chemical  agent 
in  Pharmacy. — London  Pliar.  Jour.  August  1st,  1855. 
Glasgow,  July  9th,  1855. 
NITRATE  OF  SILVER  AND  TANNIC  ACID  IN  PILLS. 
By  W.  Copney. 
Having  been  applied  to  as  to  the  propriety  of  exhibiting  these 
substances  together  in  the  form  of  pills,  some  experiments  were 
made  to  determine  the  chemical  change  which  might  occur. 
It  was  believed,  a  priori,  that  a  change  would  occur,  from  the 
well  known  tendency  of  tannic  acid  to  run  into  gallic  acid  when 
exposed  to  the  air  in  a  humid  state,  or  when  brought  into  contact 
with  oxygen  acids  or  their  compounds.  It  was  thought,  however, 
that  in  the  form  of  a  pill,  made  as  firm  as  possible,  any  change 
which  might  occur  would  not  proceed  very  rapidly.  Some  pills 
having  been  prepared,  each  composed  of  half  a  grain  of  nitrate 
of  silver  and  three  grains  of  tannic  acid,  with  a  suitable  excipient, 
it  was  observed  that  they  quickly  became  swollen  and  subsequently 
.  cracked. 
An  indication  was  thus  given  that  a  change  had  taken  place, 
which  was  supposed  to  have  arisen  from  the  absorption,  by  the 
tannic  acid,  of  oxygen  at  the  expense  of  the  nitrate,  reducing  it 
to  oxide,  with  the  formation  of  gallic  acid  ;  the  softening,-  enlarge- 
ment, and  cracking  of  the  pills  being  referred  to  the  formation 
of  water  and  the  escape  of  carbonic  acid  gas,  which  are  always 
produced  when  tannic  acid  is  converted  into  gallic  acid. 
Solutions  of  these  substances  were  then  separately  prepared 
