1 1  a  Assay  Processes  of  U.S. P.  IX.     f  AlVTou£-  Pharm- 
1  A'i-  -  '  l      March,  1917 
breaks  up  the  compound  into  the  acid  and  the  sulphate.  The  ex- 
cess of  acid  used  is  then  titrated  with  n/io  KOH. 
The  direct  titration  of  borax,  sodium  cacodylate,  sodium  glycero- 
phosphate and  others  of  this  class,  by  n  2  HC1  depends  upon  the 
property  of  the  liberated  acids  from  these  compounds  being  indif- 
ferent to  methyl  orange.  The  compounds  are  ionized  in  the  solu- 
tion, and  only  the  bases  respond  to  the  indicator. 
In  the  assay  of  chloral  hydrates,  the  compound  is  first  treated 
with  an  excess  of  normal  KOH.  This  converts  the  chloral  into 
chloroform  and  potassium  formate,  according  to  the  following  equa- 
tion : 
CCI3CHO        +       KOH       =       CHCL       4=  KC02H. 
Chloral  Potassium  Chloroform  Potassium 
Hydroxide  Formate 
The  excess  of  alkali  is  then  titrated  with  normal  sulphuric  acid. 
Several  of  the  compounds,  such  as  formaldehyde  and  parafor- 
maldehyde, are  assayed  under  the  acidimetric  method,  after  having 
been  first  oxidized  by  peroxide  of  hydrogen.  The  compound  to  be 
assayed  is  treated  with  alkali,  then  with  hydrogen  peroxide,  after 
which  the  excess  of  alkali  used  is  determined  by  titration  with  sul- 
phuric acid,  litmus  being  used  as  the  indicator. 
Only  one  of  the  compounds  of  the  U.  S.  P.  is  assayed  by  dis- 
tillation, solution  of  ammonium  acetate.  The  assay  is  carried  out 
by  adding  an  excess  of  alkali  to  the  solution.  The  mixture  is 
heated  and  the  ammonia  is  distilled  into  a  known  quantity  of  nor- 
mal sulphuric  acid.  The  excess  of  acid  used  is  determined  by  titra- 
tion with  alkali. 
Metallic  organic  salts  are  directed  to  be  assayed  by  first  car- 
bonizing the  salt.  By  this  process,  the  compound  is  converted  into 
its  carbonate.  The  cooled  mass  is  disintegrated ;  the  crucible  and 
mass  are  transferred  to  a  beaker.  Fifty  mils  each  of  water  and 
half-normal  acid  are  added  and  the  beaker  covered  with  a  watch 
crystal  and  boiled  for  thirty  minutes.  The  solution  is  filtered  and 
the  residue  washed  until  no  longer  acid  to  litmus.  The  excess  of 
acid  is  titrated  with  alkali,  with  methyl  orange  as  an  indicator. 
The  following  salts  are  assayed  by  this  method :  calcium  lactate, 
lithium  citrate,  potassium  acetate,  citrate,  potassium  and  sodium 
tartrate,  Seidlitz  powder,  sodium  acetate,  benzoate,  citrate,  salicylate, 
and  strontium  salicylate. 
