Am-Joul-  pharm-}     Assay  Processes  of  US.P.  IX. 
March,  1917      J  J  J 
121 
In  the  assay  of  oil  of  eucalyptus  another  foreign  condition  is 
met.  This  oil  contains  eucalyptol  or  cineol,  C10HlsO,  of  which  not 
less  than  70  per  cent,  by  volume  shall  be  present. 
The  assay  directs  that  10  mils  of  the  oil  be  placed  in  a  round- 
bottom  glass  dish,  imbedded  in  finely  broken  ice.  10  mils  of  arsenic 
acid  T.S.  are  added  and  stirred  until  precipitation  is  complete. 
When  the  mixture  ceases  to  congeal  further,  it  is  allowed  to  stand 
10  minutes  in  the  ice  bath.  Upon  the  expiration  of  this  time,  it  is 
transferred  to  a  hard  filter  paper  and  covered  with  another  paper, 
the  whole  being  surrounded  by  filter  papers  and  placed  between  the 
plates  of  a  press  to  remove  all  liquids.  When  completely  dry,  the 
eucalyptol  arsenate  is  transferred  to  a  cassia  flask  and  hot  water 
added,  and  the  flask  placed  in  boiling  water.  This  decomposes  the 
eucalyptol  arsenate  into  eucalyptol.  When  cool,  sufficient  water  is 
added  to  raise  the  eucalyptol  to  a  level  where  it  can  be  read. 
CHLORIDES,  IODIDES  AND  BROMIDES.  ' 
The  salts  of  chlorides,  iodides  and  bromides  are  similarly  deter- 
mined. The  weighed  amount  is  placed  in  a  200-mil  flask  and  dis- 
solved in  25  mils  of  water.  50  mils  n/10  silver  nitrate  is  added,  5 
mils  of  nitric  acid,  and  sufficient  water  to  make  200  mils.  Mix 
and  filter.  The  first  20  mils  of  the  filtrate  are  rejected.  100  mils 
of  the  filtrate,  after  treating  with  nitric  acid  and  iron  and  ammonium 
sulphate  T.S. ,  are  titrated  with  n/10  KCNS. 
Hydrocyanic  acid  and  sodium  cyanide  are  determined  by  the 
silver  nitrate  method,  with  potassium  iodide  as  an  indicator.  To  the 
HCN,  KOH  is  added.  The  silver  nitrate  produces  the  double  cy- 
anide of  silver  and  potassium,  which  is  not  affected  by  the  alkali. 
Further  addition  of  silver  causes  a  decomposition,  the  insoluble  sil- 
ver cyanide  separating;  the  silver  cyanide  then  reacts  with  the 
potassium  iodide,  forming  silver  iodide,  which  is  shown  by  the  pro- 
duction of  a  yellow  color. 
The  silver  method  is  also  used  for  the  determination  of  the 
soluble  phosphates  and  the  hypophosphites.  The  hypophosphites 
are  first  oxidized  to  the  phosphates  by  nitric  acid,  and  the  methods 
then  followed  as  under  phosphoric  acid. 
(To  be  continued.) 
