644  The  Manufacture  of  Aspirin  Tablets.    { Am-sJ°tur\ ™£rm- 
of  their  sticky  surface  allow  small  particles  to  adhere  to  the  punches 
thus  leaving  dents  in  the  surface  of  the  tablet.  This  to  the  manu- 
facturer is  known  as  "  picking,"  meaning  that  the  punches  pick  off  a 
small  particle,  leaving  a  cavity  in  the  tablet.  It  will  be  readily  seen 
from  the  physical  properties  of  aspirin  that  it  is  necessary  to  have 
present  a  binder,  or  excipient.  Sugar  has  not  proven  satisfactory 
for  this  purpose  as  sugar  itself  attracts  moisture,  and  complicates 
the  operating  of  a  compressing  machine.  It  must  also  be  remem- 
bered that  moisture  decomposes  aspirin,  and  its  presence  in  large 
quantities  is  highly  objectionable,  therefore  the  excipient  must  be 
one  that  can  be  dried  very  readily  and  that,  at  a  low  temperature. 
Glucose,  gelatin  and  tragacanth  all  fail  to  answer  on  account  of  their 
sticky  and  slow  drying  qualities.  Honey  would  not  answer  as  its 
tendency  is  to  darken  white  tablets,  and  the  need  of  much  filler 
makes  it  unsuitable.  Water  alone  will  not  bind  properly.  Solution 
of  acacia  answers  fairly  well  but  both  starch  paste  and  acacia  are 
lacking  in  making  a  fine  aspirin  tablet.  It  will,  therefore,  be  found 
that  a  weak  solution  of  white  dextrine  in  combination  with  a  filler 
of  starch  answers  better  than  any  other  excipient  for  producing  a 
mass  of  aspirin  for  proper  granulation.  It  might  here  be  explained 
for  the  information  of  the  unitiated  that  except  in  extremely  rare 
cases  it  is  never  possible  to  compress  powders  of  fine  degree,  but 
that  granules  must  be  built  up  from  the  powder. 
Another  feature  involved  in  the  preparing  of  an  aspirin  mass 
or  mixture  is  that  it  must  not  be  exposed  to  contamination  from 
metals.  From  the  samples  examined  it  is  evident  that  some  of  these 
have  been  manufactured  in  the  ordinary  iron  mixers,  or  if  granite- 
ware  containers  have  been  used  the  surface  has  not  been  perfect, 
and  iron  has  been  exposed.  If  this  is  not  the  case  the  moist  mass, 
before  drying,  has  evidently  been  forced  through  a  brass,  or  an  iron 
screen,  which  has  produced  contamination,  and  resultant  discolora- 
tion. In  this  particular  product  the  writer  has  found  nothing  more 
satisfactory  than  the  mixing  of  the  aspirin  ingredients  in  a  special 
wooden  tub  made  of  maple.  The  operator  may  mix  the  dry  ingre- 
dients through  a  properly  protected  powder  mixer,  but  the  addition 
of  the  dextrine  solution  must  be  made  in  these  wooden  tubs,  the 
operator  wearing  long  rubber  gloves.  Care  should  be  exercised  in 
all  cases  that  the  minimum  amount  of  moisture,  for  the  best  results 
to  be  obtained,  shall  be  strictly  adhered  to.   The  finished  mass  taken 
