120  Assay  Processes  of  US. P.  IX.     {AnVJouf-  Pharm- 
A    w  J  J  l       March,  1 9 17 
hydroxide.  Two  drops  potassium  chromate  are  added,  and  then 
sufficient  silver  nitrate  to  produce  a  red  tint.  To  the  mixture  thus 
prepared  a  weighed  quantity  of  the  oil  to  be  tested  is  then  added  and 
titrated  with  n  10  silver  nitrate. 
Oil  of  lemon.  The  aldehyde  present  in  this  oil  is  citral, 
C10H16O  (M.  W.  152.13),  of  which  it  should  contain  not  less  than 
4  per  cent.  Its  method  of  assay  is  similar  to  that  of  benzaldehyde, 
with  but  slight  modifications. 
Eugenol.  ally!  guaiacol.  C6H3OCH3CH3OH.  Several  of  the  offi- 
cial oils,  such  as  cloves,  allspice,  etc.,  contain  this  principle.  The 
assay  is  readily  carried  out  by  placing  10  mils  of  the  oil  in  a  cassia 
flask  and  shaking  for  5  minutes,  after  which  it  is  heated  for  10 
minutes  on  a  water  bath,  cooled,  the  liquid  allowed  to  separate  and 
sufficient  KOH  added  to  raise  the  lower  level  of  the  oil  within  the 
graduated  part  of  the  neck,  and  noting  the  volume  of  residual  liquid. 
The  alkali  converts  the  phenol  into  a  soluble  sodium  compound. 
Oil  of  thyme  should  contain  not  less  than  20  per  cent,  by  volume 
of  phenol.    Its  assay  is  like  the  above. 
Oil  of  mustard  presents  a  method  of  assay  different  from  all 
others.  It  owes  its  property  to  allyl-isothiocyanate,  C3H5SCN,  of 
which  not  less  than  92  per  cent,  should  be  present.  4  mils  of  the 
oil,  accurately  weighed,  are  diluted  with  alcohol  to  make  exactly 
100  mils.  5  mils  of  this  solution  are  placed  in  a  100  mil  flask,  and 
50  mils  of  11  10  silver  nitrate  are  added,  and  5  mils  of  ammonia 
water.  The  flask  is  connected  with  a  reflux  condenser  and  heated 
for  one  hour.  After  cooling,  it  is  made  up  with  water  to  100  mils, 
mixed  and  filtered.  50  mils  of  the  filtrate,  after  treating  with  nitric 
acid  and  iron  indicator,  is  titrated  with  KCXS.  The  allyl-isothio- 
cyanate is  converted  by  the  ammonia  into  thiosinamine : 
C3H5NCS         +         NH3         =  C3H5NHNH_XS. 
AIM-  Ammonia  Thiosinamine 
isothiocyanate 
The  action  of  the  silver  oxide  produced  by  adding  ammonia  water 
to  silver  nitrate,  removes  the  sulphur  as  silver  sulphide,  with  the 
formation  of  allyl-cyanamide : 
CH3XHXHXS  +  Ag20  =  Ag2S  +   CNNHC3Hg  +  H20. 
isothiocyanite'  Silver        Sulphide  Allyl-cyanamide 
Oxide  Silver 
