32  Chemical  Observations  on  Tartar  Emetic.    {Am  jja™yil£arm' 
temperature  causes  a  decrease  in  the  specific  rotation  of  this  com- 
pound. 
It  is  a  remarkable  fact  that  a  solution  of  tartar  emetic  possesses  a 
much  greater  specific  rotation  than  a  corresponding  solution  of  any  of 
the  commonly-occurring  tartrates.  For  acid  tartrate  of  potassium,  for 
instance,  [a  ]D=  -f-  22*61°.  The  high  specific  rotation  is  therefore 
characteristic  of  tartar  emetic,  and  might  be  usefully  employed  as  a 
test  for  the  purity  of  salt.  Thus  we  have  found  that  an  admixture  of 
five  per  cent,  of  acid  tartrate  of  potassium  with  tartar  emetic  reduces 
the  rotatory  power  of  a  4  per  cent,  solution  of  the  salt  to  +10*6°  (200 
mm.  at  15° C.)  that  is  for  [a  ]D  + 132-5°. 
By  means  of  its  action  on  polarized  light  a  solution  of  tartar  emetic 
may  readily  be  distinguished  from  any  of  the  double  oxalates  of  anti- 
mony and  potassium,  which  are  used  in  dyeing  as  substitutes  for  tar- 
tar emetic,  since  solutions  of  these  salts  are  devoid  of  action  on  polar- 
ized light. 
4.     AN  EXAMINATION  OF  COMMERCIAL  SPECIMENS. 
It  seemed  to  be  of  interest  to  determine  the  purity  of  the  tartar 
emetic  employed  in  medicine.  Twelve  specimens  were  purchased 
from  pharmacists.  The  antimony  was  estimated  by  titration  of  the 
dissolved  salt  with  a  standard  solution  of  iodine  in  the  manner  pre- 
viously described.   The  results  were  as  follows  : — 
Analyses  of  Commercial  Specimens  of  Tartar  Emetic. 
No.  of        Weight  of  salt         Weight  of  salt  Percentage  of 
specimens.          taken.  found.  (SbOKC4H406,^H20). 
1                    0-236  0-2415  102'3 
2                    0  3515  0-3554  101*1 
3                    0-2584  0-2608  100:9 
4                    0-2218  0-2221  1001 
5                    0-2511  0-2491  99*2 
6                    0-2649  0-2633  99-4 
7                    0-3373  0-3336  987 
8                     0-2602  0-2562  98"4 
9                    0  2894  0  2825  97*6 
10                    0  2305  0-2235  96*9 
11                    0-2539  0-2426  95*5 
12                    0  2434  0*2305  947 
It  will  be  seen  that  many  of  these  specimens  are  of  such  purity  as 
one  might  reasonably  look  for  in  commerce.    It  is  noticeable,  how- 
