412 
Quinine  Testing. 
(  Am.  Jour.  Pharm. 
\      August,  1887. 
is  optional  which  mode  of  testing  is  applied  for  ascertaining  the 
amount  of  cinchonidine  sulphate  in  the  quinine  sulphate  of  commerce. 
I  may  mention  here  that  the  compound  of  quinine  and  cinchonidine 
obtained  in  applying  the  bisulphate  test  to  commercial  quinine  sul- 
phate will  also  contain  hydroquinine,  and  probably  also  in  some  cases 
hydrocinchonidine  and  homocinchonidine  in  small  proportions,  so 
that  if  the  crystals  separated  were  tested  for  quinine  by  the  optical 
method  it  would  give  results  decidedly  too  low.  This  is  less  to  be 
feared  with  the  recrystallization  test,  because  hydroquinine,  which  has 
the  greatest  influence  on  the  result  of  the  optical  test,  would  not  be 
concentrated  in  the  mother-liquors. 
De  Vrij's  bichromate  test  is  quite  unsuited  for  the  quantitative  de- 
termination of  cinchonidine,  though  it  admits  of  its  presence  being  de- 
tected when  it  amounts  to  only  0*3  per  cent.  The  reason  of  this  is 
that  as  the  amount  of  cinchonidine  increases,  more  or  less  of  it  is  pre- 
cipitated with  the  quinine  chromate.  It  is  probably  on  this  account 
that  in  applying  the  test  to  a  sulphate  containing  2*7  per  cent,  cin- 
chonidine sulphate,  as  Schlickum  recommends,  I  did  not  obtain  im- 
mediate indications  of  the  presence  of  cinchonidine,  and  only  a  few 
crystals  were  formed  after  the  lapse  of  an  hour.  The  crystals  ob- 
tained by  this  test  also  contaiu  quinine,  and  are  a  compound  of  qui- 
nine with  seven  molecules  of  cinchonidine. 
This  is  also  the  case  with  the  oxalate  test,  and  what  Schafer  origin- 
ally took  for  pure  cinchonidine  contains  quinine,  as  he  has  since  ad- 
mitted. The  amount  appears  to  be  considerable,  as  I  infer  from  the 
fact  that  when  dissolved  with  excess  of  sulphuric  acid  the  solution  has 
a  strong  fluorescence,  and  it  becomes  intensely  green  when  mixed  with 
chloride  of  lime  and  ammonia. 
According  to  the  directions  for  applying  this  test  the  precipitate 
formed  on  adding  soda  solution  to  the  filtrate  from  the  quinine 
oxalate  is  not  to  be  collected  until  after  twelve  hours,  and  for  each 
100  c.c.  of  liquid  an  addition  of  0*04  gm.  is  to  be  made  to  the  weight 
of  the  precipitate  as  a  correction  for  the  cinchonidine  remaining  in 
solution.  When  the  amount  of  cinchonidine  exceeds  4  per  cent.,  the 
addition  is  to  be  0*066  gm.,  and  the  concentration  of  the  solution 
must  be  kept  to  1  in  50. 
Objection  has  been  made  from  several  quarters  to  this  test  that  too 
little  potassium  oxalate  is  used  for  precipitating  the  quinine.  But 
that  is  not  the  case,  for  normal  potassium  oxalate  has  only  one  mole- 
