A^JJa0nuylmarBa•}     Chemical  Observations  on  Tartar  Emetic.  27 
CHEMICAL  OBSERVATIONS  ON  TARTAR  EMETIC.1 
By  Prof.  Dunstan  and  Miss  L.  E.  Boole. 
Communication  from  the  Research  Laboratory  of  the  Pharmaceutical  Society. 
1.     ON  SOME  STATEMENTS  IN  THE  BRITISH  PHARMACOPOEIA. 
For  the  determination  of  the  antimony  in  tartar  emetic  the  phar- 
macist may  be  supposed  to  rely  on  the  process  described  in  the  British 
Pharmacopoeia.  "  Twenty-nine  grains  dissolves  (sic)  slowly  but  with- 
out residue  in  a  fluid  ounce  of  distilled  water  at  60°  F.  (15*5°  C),  and 
the  solution  gives  with  sulphuretted  hydrogen  an  orange  precipitate 
which  when  washed  and  dried  at  212°  F.  (100°  C.)  weighs  15*1 
grains." 
These  instructions  stand  in  need  of  considerable  amendment  to  ren- 
der them  of  any  service  in  practice.  Unless  the  solution  is  first 
acidified,  oxy-salt  is  invariably  carried  down  with  the  sulphide,  and 
this  together  with  free  sulphur,  will  cause  the  result  to  be  higher  than 
that  which  is  demanded  by  the  known  composition  of  the  salt.  Acid 
tartrate  of  potassium  is  also  precipitated,  and  it  is  difficult  to  remove 
the  whole  of  this  salt  from  the  precipitate  unless  it  is  washed  with  an 
unusually  large  quantity  of  water.  Further,  it  is  extremely  difficult 
to  filter  the  finely  divided  sulphide,  in  fact,  it  is  almost  impossible  to 
do  so,  unless  the  liquid  containing  the  precipitate  is  boiled  for  some 
time ;  but  this  generally  leads,  when  free  acid  is  present,  to  the  de- 
composition of  some  of  the  sulphide,  and  in  this  way  error  is  intro- 
duced. Again,  antimony  sulphide  cannot  be  completely  dried  at 
100°  C.  A  small  quantity  of  water,  about  two  per  cent.,  is  obsti- 
nately retained,  and  is  only  lost  with  difficulty  at  a  higher  tempera- 
ture ;  indeed,  according  to  Fresenius,  even  at  a  higher  temperature  a 
current  of  carbon  dioxide  is  necessary  to  effect  its  entire  expulsion.  It 
is  chiefly  for  these  reasons  that  chemists  in  general  have  long  since 
abandoned  the  method  of  directly  weighing  the  antimony  sulphide, 
and  yet  the  process  is  adopted,  as  a  test  of  purity,  in  the  British 
Pharmacopoeia  without  any  allusion  to  these  various  sources  of  inac- 
curacy. Lastly,  it  should  be  observed  that  the  amount  of  antimony 
sulphide  represented  by  the  Pharmacopoeia  as  obtainable  from  29 
1  Read  before  the  Pharmaceutical  Society  of  Great  Britain  at  an  Evening 
Meeting  in  London,  Wednesday,  November  14,  reprinted  from  Phar.  Jour,  and 
Trans.,  Nov.  17. 
