44      PURITY  OF  SULPHATE  OF  QUININE  OF  COMMERCE. 
trustworthy  of  any  hitherto  submitted.  The  reagent  is  sulpho- 
cyanide  of  potassium. 
Into  an  ounce  of  distilled  water  drop  ten  drops  of  dilute  sul- 
phuric acid  (British  Pharmacopoeia  /g).  To  thi3  add  14  grains 
(or  as  much  as  will  saturate  the  acid)  of  the  suspected  salt. 
Filter  through  paper,  and  to  a  little  of  the  filtered  solution  add 
a  few  drops  of  the  solution  of  sulphocyanide  of  potassium  (180 
grains  in  li  ounces  of  water).  An  immediate  precipitate  of 
the  several  alkaloids  takes  place,  each  of  which,  as  seen  by  the 
sketches,  is  distinct  and  characteristic. 
If  quinine,  quinidine,  and  cinchonine  be  present  they  will 
all  be  seen  on  the  slide  distinct  from  each  other,  becoming  more 
so  every  minute. 
A  very  good  plan  is  to  place  a  very  small  drop  on  a  glass  slip 
and  to  put  another  of  the  sulphocyanide  by  its  side.  Over  both 
place  a  piece  of  thin  glass,  which  will  cause  the  drops  to  touch. 
Examine  the  line  of  junction  under  a  quarter-inch  lens,  when 
the  crystals  are  seen  and  may  be  readily  recognized.  By  this 
method  10000  °f  a  grain  of  quinidine  or  cinchonine  may  easily 
be  detected. 
It  is  very  interesting  to  see  the  particles  all  arranging  them- 
selves into  the  respective  groups ;  the  long  slender  needles  of 
the  quinine  salt,  the  round  crystalline  masses  of  the  quinidine, 
Sulphocyanide  of  quinine.         Sulphocyanide  of  quinidine.         Sulphyocyanide  of  cinchonine 
(450  diam.)  (450  diam.)  (460  diam.) 
and  the  large  well-formed  prisms  of  the  cinchonine  salts.  So 
remarkably  constant  is  this  reaction,  that  an  observer  who  has 
once  been  accustomed  to  the  general  appearance  can  at  once 
say  with  ease,  this  is  quinine,  this  quinidine,  and  that  cin- 
chonine. 
