Am*jJa0nuyi£9arm'}     Chemical  Observations  on  Tartar  Emetic.  31 
onate  is  quite  definite,  and  may  be  utilized  as  the  basis  of  a  volumetric 
operation  in  which  solutions  of  tartar  emetic,  with  sodium  bicarbonate, 
are  titrated  with  a  decinormal  solution  of  iodine  in  the  usual  manner. 
3.     ACTION   OF  ALCOHOL   ON  AN  AQUEOUS   SOLUTION  OF  TARTAR 
EMETIC. 
When  alcohol  is  added  to  an  aqueous  solution  of  tartar  emetic  a 
white  precipitate  is  produced.  This  has  been  alleged  to  consist  either 
of  finely  divided  hydrous  crystals  or  perhaps  of  the  anhydrous  salt. 
The  use  of  anhydrous  salt  in  quantitative  experiments  such  as  we 
have  conducted  is  of  much  assistance,  since  the  hydrous  crystals  are 
liable  to  alter  their  composition,  owing  to  efflorescence.  We  therefore 
investigated  the  composition  of  this  precipitate  after  it  had  been 
quickly  dried,  first  at  50°  C,  and  finally  in  a  partial  vacuum,  over 
calcium  chloride.  The  white  powder  was  dissolved  in  water  and  the 
liquid  was  titrated  with  a  solution  of  iodine.  The  results  obtained 
were  as  follows  : — 
Weight  of  salt  Weight  of  salt  found,  calculated  as 
taken.  SbOKC4H406. 
0-1656  0-1657 
0-4960  0-4957 
They  prove  that  the  precipitate,  prepared  as  above  described,  is  en- 
tirely constituted  of  anhydrous  tartar  emetic. 
3.     THE  SPECIFIC  ROTATION  OF  AQUEOUS  SOLUTIONS. 
The  action  of  aqueous  solutions  of  tartar  emetic  on  polarized  light  is 
very  rarely  alluded  to  in  treatises  on  chemistry.  Solutions  of  the  salt 
are  powerfully  dextro-rotatory.  Determinations  of  the  specific  rota- 
tion have  been  made  by  Landolt  and  by  Krecke.  Landolt  found 
that  7*982  of  anhydrous  tartar  emetic  dissolved  in  100  cc.  of  water  ef- 
fected at  20°  C.  an  amount  of  rotation  equivalent  to  [a  ]D=  +142*76°. 
Krecke  found  that  a  five  per  cent,  solution  of  tartar  emetic  at  25°  C. 
effected  a  rotation  corresponding  to  [a ]D=  +138*66°.  We  have 
made  several  determinations  at  15°  C.  with  a  four  per  cent,  solution 
of  the  crystallized  salt,  using  a  tube  200  mm.  long.  The  angle  of  ro- 
tation under  these  conditions  is +11*3°,  whence  [a  ]  D=  +141*25°, 
and  for  the  anhydrous  salt  under  the  same  conditions  +11*4,  whence 
[a  ]D=  +142*5°.  This  result  is  probably  in  agreement  with  that  ob- 
tained by  Krecke  at  25°  C,  since  it  is  known  that  an  increase  of 
