AmMJa0r^;^rm-}     Literature  Relating  to  Pharmacy.  157 
in  the  manufacture  of  caustic  at  the  Calcutta  Medical  Depot.  The 
silver  employed  always  contains  a  certain  amount  of  copper,  and 
after  solution  of  the  metal  in  nitric  acid  and  separation  of  the  gold, 
as  much  as  possible  of  the  nitrate  of  silver  is  crystallized  out,  and 
the  deep  blue  mother  liquor  evaporated  to  dryness.  The  dry  salt 
is  then  powdered  and  placed  in  a  glass  funnel,  stopped  with  a  plug  of 
asbestos,  and  percolated  with  strong  nitric  acid,  specific  gravity  1-42. 
The  nitric  acid  dissolves  the  whole  of  the  nitrate  of  copper,  leaving 
the  nitrate  of  silver  perfectly  white,  while  only  a  very  small  amount 
of  the  latter  salt  is  dissolved.  The  nitric  acid  can,  of  course,  be  re- 
covered by  distillation,  and  the  small  amount  of  nitrate  of  silver 
separated  from  the  nitrate  of  copper  by  precipitation  with  salt,  and, 
when  sufficient  has  accumulated,  reduced  to  the  metallic  condition 
by  one  of  the  usual  methods.  In  preparing  nitrate  of  silver  by 
crystallizing  out  the  salt,  a  point  is  reached  when  the  mother  liquor 
is  too  highly  charged  with  nitrate  of  copper  to  permit  of  a  suffi- 
ciently pure  silver  salt  separating  by  crystallization,  and  this  impure 
or  "  blue  nitrate  of  silver"  has  hitherto  been  returned  to  the  mint. 
By  the  adoption,  however,  of  the  method  above  described,  these 
residues  can  be  worked  up  and  nearly  the  whole  of  the  silver 
obtained  in  the  form  of  nitrate,  and  as  the  nitric  acid  can  be  recov- 
ered the  process  is  decidedly  economical,  while  it  affords  a  salt 
practically  free  from  copper. 
TONKA  BEANS. 
The  following  information  concerning  this  drug  is  furnished  by 
Superintendent  J.  H.  Hart,  of  the  Royal  Botanic  Gardens,  Trinidad, 
in  the  Bulletin  of  Miscellaneous  Information  for  January,  1897, 
p.  11. 
The  tonga,  tonquin  or  tonka  bean  is  the  product  of  a  tree  known 
to  botanists  as  Dipterix  odorata,  Willd.,  and  less  frequently  as  the 
Coumarouna  odora  of  Aublet.  The  latter,  however,  is  given  in  the 
Kew  Index  as  the  nomen  prius. 
The  tree  thrives  well  in  Trinidad  when  planted  in  shady,  damp 
situations,  and  is  very  abundant  in  the  forest  of  the  neighboring 
mainland  of  Venezuela.  The  fruit  or  seed  ripens  in  June  and  July, 
and  in  these  months  large  shipments  are  received  in  Trinidad 
from  South  American  ports.  In  the  newspaper  of  July  10,  1896, 
the  arrival  is  reported  of  a  consignment  of  260  bags  "  Tonca  Beans," 
