172 
Assay  Processes. 
Am.  Jour.  Pharm. 
April,  1917. 
with  control  tubes.  The  nitrometer  is  completely  filled  with  sat- 
urated salt  solution,  care  being  taken  that  no  air  is  present.  When 
ready  the  control  tube  is  placed  at  a  low  level.  The  substance  to 
be  assayed  is  first  prepared  by  adding  to  it  potassium  bicarbonate, 
to  remove  any  acid  that  may  be  present.  The  quantity  of  material 
to  be  assayed  is  added  to  the  nitrometer,  followed  by  potassium 
iodide  and  sulphuric  acid.  The  whole  is  shaken,  and  after  the  reac- 
tion has  ceased,  the  equilibrium  tube  is  raised  to  the  level  of  the 
liquid  in  the  nitrometer  and  the  reading  taken.  Temperature  and 
barometric  pressure  should  also  be  considered. 
C2H5N02  +  KI  +  H2S04  =  C2H5OH  +  KHS04  +  I  +  NO. 
Ethyl      Potassium  Sulphuric        Alcohol         Potassium  Iodine  Nitric 
Nitrite         Iodide        Acid  Bisulphate  Oxide 
The  purity  of  oxygen  is  determined  by  placing  fifty  mils  of  it 
into  an  accurately  calibrated  tube,  with  10  mils  of  alkaline  pyro- 
gallol  solution;  not  less  than  95  per  cent,  by  volume  should  be  ab- 
sorbed. 
MISCELLANEOUS  ASSAYS. 
The  refractometer  is  directed  to  be  used  in  determining  the 
purity  of  several  of  the  volatile  oils. 
The  polariscope  is  used  principally  in  the  testing  of  volatile  oils. 
Its  use  is  also  directed  in  the  assay  of  spirits  and  liniment  of 
camphor. 
The  assay  is  conducted  by  taking  the  mean  of  4  polariscopic 
readings  of  the  spirit  in  a  200  Mm.  tube.  Correction  to  be  made 
for  temperature.  60  mils  of  the  spirits  is  also  evaporated  on  a 
water  bath,  and  when  the  camphor  begins  to  solidify,  it  is  stirred 
until  dry.  The  camphor  is  then  placed  on  a  watch  crystal,  covered 
with  an  inverted  funnel,  and  heated  by  a  Bunsen  burner  to  sublime 
the  camphor.  2.5  Gm.  of  the  sublimate  are  dissolved  in  sufficient 
95  per  cent,  alcohol  to  make  exactly  25  mils,  and  the  mean  of  four 
polariscopic  readings  are  taken.  The  minutes  of  rotation  of  the 
spirits  divided  by  the  minutes  of  rotation  of  control,  multiplied  by 
10  gives  the  grams  of  camphor  in  a  hundred  mils  of  the  spirit. 
SAPONIFICATION. 
Saponification  methods  are  used  in  the  U.  S.  P.  in  assaying  fats, 
resins,  wax,  and  volatile  oils.  The  saponification  value  indicates 
the  number  of  Mgs.  of  KOH  required  to  saponify  one  gram  of 
