28  Chemical  Observations  on  Tartar  Emetic.™  {Am- j£nT/im&Tm' 
grains  of  tartar  emetic  is  15*1  grains,  whereas  the  quantity  demanded 
by  the  formula  of  the  salt  (SbOKC4H406,  iH20)  is  only  14*67 
grains. 
2.     THE  VOLUMETRIC  ESTIMATION  OF  THE  ANTIMONY  IN  TARTAR 
EMETIC. 
Having  regard  to  the  extensive  employment  of  tartar  emetic  in 
medicine,  it  is  clearly  desirable  that  a  trustworthy  and  simple  method 
for  its  quantitative  analysis  should  be  available  for  use  by  the  phar- 
macist. A  volumetric  process  has  been  proposed  which  involves  the 
use  of  standard  solutions  of  bleaching'  powder  and  potassium  arsenite. 
For  the  pharmacist  this  process  is  inconvenient,  since  it  necessitates 
the  employment  of  two  volumetric  solutions  which  must  be  specially 
prepared. 
It  seemed  worth  while  to  attempt  to  utilize,  for  a  volumetric  pro- 
cess, the  decolorization  of  a  solution  of  iodine,  which  is  effected  by  a 
solution  of  tartar  emetic,  on  the  basis  of  the  reaction 
SbOK-C4H406+I2+2H20-=2HI+KHC4H406-f-HSb03. 
Mohr  had  already  proposed  to  utilize  this  oxidation  as  a  volumetric 
operation  applicable  to  antimonious  compounds,  and  on  his  recom- 
mendation the  process  is  not  infrequently  described  in  treatises  on  vol- 
umetric analysis.  The  method  has  been  tested  by  Fresenius,  whose 
results  were  not  quite  satisfactory,  being  in  general  slightly  too  high- 
It  appeared  desirable  that  a  further  trial  of  the  method  should  be 
made. 
Tartar  emetic  was  several  times  crystallized  from  water,  and  the 
crystals  dried  by  exposure  in  a  partial  vacuum.  To  establish  the 
purity  of  these  crystals  the  amount  of  potassium  was  determined.  As 
this  proved  to  be  a  troublesome  operation,  it  may  be  well  to  give 
some  account  of  the  different  experiments  which  were  made,  as  well  as 
of  the  method  finally  adopted.  In  order  to  separate  the  potassium  it 
was  necessary  first  to  remove  the  whole  of  the  antimony  from  a  solu- 
tion of  the  salt.  Many  attempts  were  made  to  effect  this  removal  by 
means  of  hydrogen  sulphide,  but  these  failed,  chiefly  for  reasons  which 
have  already  been  alluded  to.  ^Neither  was  it  found  practicable  to  re- 
move the  antimony  by  the  evaporation  of  a  solution  acidified  with  hy- 
drochloric acid,  since  a  small  quantity  of  antimony  was  dissolved  when 
the  residue,  left  on  ignition,  was  boiled  with  water.    Simple  ignition 
