AmMa??i886arm"}^armaceM^ca^  Notes  from  Purdue  University.  231 
V.    Calx  Sulphubata. — by  m.  jay. 
The  Pharmacopoeia  specifies  that  this  preparation  shall  contain  at 
least  36  per  cent,  of  CaS,  but  the  directions  for  testing  with  sulphate 
of  copper  are  very  misleading.  Lime  itself  precipitates  copper  from 
its  solution;  hence,  dilute  acid  should  be  added  with  the  pharma- 
copoeial  test,  in  order  to  dissolve  any  copper  not  precipitated  as  sul- 
phide. Even  then,  we  only  learn  whether  or  not  the  sample  contains 
less  than  the  required  percentage,  while  a  little  additional  trouble 
ensures  results  by  which  different  samples  can  be  accurately  com- 
pared. 
Tests  were  made  of  several  published  volumetric  methods  for  esti- 
mating sulphides,  depending  upon — 
1.  Complete  precipitation  by  solution  of  zinc. 
2.  Reduction  of  ferric  to  ferrous  sulphate,  and  titration  with  per- 
manganate. 
3.  Partial  precipitation  of  an  arsenite  as  As2S3,  and  titration  of 
residual  arsenic. 
Decinormal  solutions  were  prepared  containing — 
Sulphate  of  zinc  dissolved  in  excess  of  ammonia  (14.345  gnu 
ZnS04.7H20  to  the  liter); 
Permanganate  of  Potassium  (adjusted  to  be  equivalent  to  decinor- 
mal oxalic  acid) ; 
Iodine;  and 
Hydrochloric  acid. 
Other  solutions  used  were — 
Dilute  sulphide  of  ammonium,  freshly  made,  of  which  20  c.  c. 
were  used  for  each  titration ; 
Alkaline  solution  of  arsenious  acid,  of  about  1  per  cent. ;  and 
Bicarbonate  of  soda  of  known  strength. 
1.  Sulphate  of  zinc  was  cautiously  added  from  a  burette  to  20  c.  c. 
of  sulphide  of  ammonium.  A  drop  of  the  mixture  was  placed  upon 
filter  paper  from  time  to  time,  close  to  a  spot  moistened  with  test 
solution  of  acetate  of  lead;,  and  when  no  dark  stain  was.  at  once 
produced  by  contact  of  the  fluids,  the  reaction  was  considered  com- 
plete. A  stain  was  noticed  after  drying  some  minutes,  even  when 
the  zinc  was  in  excess.  As  the  mean  of  two  concordant  titrations, 
14.85  c.  c.  of  decinormal  zinc  solution  were  required  for  complete  de- 
composition of  the  sulphide. 
