Am.  Jour.  Pharnj.  \ 
August,  1887.  / 
Quinine  Testing. 
413 
cule  of  water,  and  with  quinine  sulphate  containing  15  per  cent,  water 
0*42  gram  oxalate  would  be  requisite,  or  with  completely  effloresced 
sulphate  0*47  gm. 
Another  defect  of  the  oxalate  test  is  in  the  direction  as  to  time. 
With  60  c.c.  of  liquid  half  an  hour  is  not  sufficient  for  obtaining  a 
temperature  of  20°  C.  throughout  the  whole  mass,  and  this  is  still 
more  the  case  with  larger  quantities.  For  this  reason  I  have  always 
allowed  one  hour. 
Quinine  oxalate  is,  as  Schafer  states,  almost  insoluble  in  the  pres- 
ence of  potassium  oxalate,  while  cinchonidine  oxalate  is  readily  soluble. 
When  a  cold  saturated  solution  of  quinine  oxalate  is  mixed  with  the 
proper  quantity  of  potassium  sulphate  and  an  excess  of  potassium 
oxalate,  the  quinine  oxalate  is  at  once  separated  so  completely  that 
caustic  soda  gives  no  precipitate  in  the  filtrate.  On  warming  the 
oxalate  dissolves,  but  it  separates  again  completely  on  cooling.  If, 
however,  one  per  cent,  of  cinchonidine  sulphate  be  added,  and  the  liquid 
again  warmed,  a  very  much  smaller  quantity  of  quinine  oxalate 
separates  on  cooling  than  in  the  former  case,  showing  that  the  presence 
of  cinchonidine  exercises  a  solvent  influence  on  the  quinine  oxalate. 
It  is  evident,  therefore,  that  in  operating  upon  a  mixture  a  certain 
portion  of  quinine  remains  in  the  mother  liquor,  and  consequently  the 
precipitate  produced  in  such  a  solution  by  caustic  soda  is  not  pure 
cinchonidine.  Moreover,  cinchonidine  is  precipitated  with  the  quinine 
oxalate,  and  in  both  cases  the  proportions  thus  escaping  separation 
appear  to  be  determined  by  accidental  conditions.  Hence  it  is  not 
possible  to  estimate  from  the  precipitate  produced  whether  the  cin- 
chonidine salt  amounts  to  2  per  cent,  or  only  05  per  cent,  without  a 
quantitative  determination. 
Assuming  that  in  operating  upon  quinine  sulphate  containing  0*5 
per  cent,  cinchonidine  salt,  the  precipitate  obtained  after  twelve  hours 
is  0*001  gm.  (it  is  really  rather  more)  the  addition  to  be  made  to  this 
for  60  c.c.  of  solution  would  be  0*024,  and  the  2  gm.  would  accord- 
ingly appear  to  contain  0*025  of  pure  cinchonidine,  or  1*685  per  cent, 
of  sulphate,  at  least  three  times  as  much  as  the  salt  actually  contained. 
A  direct  experiment  under  these  conditions  gave  1*77  per  cent.  The 
result  is  still  more  unsatisfactory  when  the  amount  of  cinchonidine 
salt  is  larger,  and  the  concentration  of  one  to  fifty  has  to  be  kept  to. 
In  operating  with  a  mixture  of  1*875  of  quinine  sulphate  and 
0*125  cinchonidine  salt,  corresponding  to  6*25  per  cent.,  the  result 
