302     ON  SOME  PREPARATIONS  OF  THE   U.  S.  PHARMACOPOEIA. 
more  or  less  contaminated  with  matter  held  in  solution  by  the 
chloroform,  and  which  gives  it  a  darker  color  than  the  other 
portion,  and,  consequently,  there  is  a  slight  want  of  uniformity 
in  the  product.  By  recrystallization  from  a  filtered  alcoholic 
solution,  a  purer  product  is  obtained. 
Sulphate  of  Atropia  is  made  by  the  process  of  Le  Maitre, 
and  is  based  on  the  fact  that,  whilst  atropia  is  soluble  in  ether, 
its  sulphate  is  not  ;  and,  hence,  when  the  constituents  are 
brought  together  in  that  menstruum,  the  resulting  salt  separates 
in  a  solid  semicrystaliine  form  the  ether  retaining  any  excess 
of  acid  or  alkali.  The  former  custom  of  physicians  to  pre- 
scribe atropia,  and  direct  the  apothecary  to  dissolve  it  in  water 
by  aid  of  a  sufficient  quantity  of  sulphuric  acid,  in  some  cases 
led  to  the  production  of  an  acid  solution  irritating  to  the  eyes. 
Bismuthi  Subcarbonas. — The  manipulation  in  this  process 
is  mainly  to  free  the  salt  from  arsenic.  When  bismuth  contam- 
inated with  arsenic  is  treated  by  nitric  acid,  both  metals  are 
obtained  in  solution,  the  latter,  probably,  as  arsenic  acid.  The 
filtered  solution,  on  dilution,  is  converted  into  subnitrate, 
which  precipitates,  and  acid  nitrate,  which  remains  in  so- 
lution, as  in  the  old  process.  The  precipitated  subnitrate 
would  be  contaminated  with  arsenic  acid  as  arseniate  of 
bismuth,  were  it  not  for  the  direction  to  let  the  solution  stand 
twenty-four  hours  after  diluting  it  to  the  point  when  a  further 
dilution  will  throw  down  subnitrate.  During  this  time  the 
arseniate  of  bismuth  falls  and  is  separated  by  filtering.  The 
addition  of  the  ammonia  decomposes  the  super  salt  and  increases 
the  amount  of  subnitrate  of  bismuth  obtained.  The  washed  sub- 
nitrate is  now  redissolved  in  nitric  acid,  affording  a  solution  of 
bismuth  free  from  the  contaminating  metal,  which  is  diluted  to 
the  verge  of  precipitation,  and  then  mixed  with  the  solution  of 
carbonate  of  soda  to  produce  the  subcarbonate  of  bismuth, 
which  is  washed,  pressed  and  dried.  In  this  last  operation,  it 
must  be  remembered,  the  bismuth  solution  is  added  to  the  car- 
bonate of  soda  in  excess,  which  further  insures  the  absence  of 
arsenic.  Dr.  Squibb  and  Mr.  Maisch  suggested  the  improve- 
ments in  this  process. 
Bismuthi  Subnitras. — In  this  formula  a  subcarbonate  is  formed 
