304  The  U.S. P.  Inorganic  Chemicals.  \^mi^x;S:x™' 
both  the  manufacturer  and  consumer.  The  tests  described  under 
many  of  the  chemicals  left  one  in  doubt  as  to  the  percentage  purity- 
required.  Therefore,  in  order  to  secure  uniformity  and  to  avoid 
misconstruction  of  the  intentions  of  the  text,  the  Purity  Rubric  was 
adopted  for  all  inorganic  chemicals.  The  following  represents  an 
outline  of  the  general  changes  adopted  : — 
(1)  It  was  resolved  to  ignore  the  presence  of  all  innocuous  im- 
purities which  usually  occur  in  small  quantities  in  medicinal  chem- 
icals, so  long  as  the  substance  otherwise  complied  with  the  limits  of 
purity  demanded. 
For  example,  the  presence  of  chlorids,  sulfates,  sodium  or  calcium 
in  the  salts  of  the  alkalies.  If  a  potassium  bromid  contains  of  the 
pure  salt  97  per  cent.,  or  potassium  acetate  98  per  cent.,  or  potassium 
carbonate  94  per  cent.,  it  is  immaterial,  so  far  as  their  medicinal 
uses  are  concerned,  whether  they  contain  these  harmless  impurities 
or  not. 
(2)  To  drop  all  flame  tests  for  the  presence  of  sodium  in  potassium 
salts.  This  extremely  sensitive  test  demands  a  degree  of  purity 
which  is  practically  unattainable  and  unnecessary. 
(3)  To  establish  the  limit  of  purity  of  each  chemical,  which  is 
to  be  stated  (as  rubric)  in  long  primer  type  directly  under  the 
title. 
(6)  To  revise  the  tests  (with  reference  to  uniformity  and  sensitive- 
ness) for  the  presence  of  poisonous  metals.  This  is  more  particu- 
larly applicable  to  those  chemicals  which  are  administered  frequently 
and  in  large  doses  extending  over  longer  periods  of  time.  For  ex- 
ample, such  salts  as  sodium  phosphate,  the  hypophosphites,  sulfates, 
acetates,  etc.  Furthermore, 
(7)  Estimation  of  Organic  Salts  of  the  Alkalies. — In  the  estimation 
of  the  organic  alkali  salts,  instead  of  employing  a  molecular  quan- 
tity of  the  chemical  as  was  directed  in  the  U.S. P.  1890,  whereby 
the  number  of  cubic  centimeters  of  volumetric  solution  consumed 
represented  the  percentage  purity,  an  even  quantity,  namely  1 
gramme,  has  been  adopted  in  the  present  revision.  With  the  atomic 
weight  system  (H  —  1)  as  at  present  adopted,  the  former  plan  was 
found  to  be  objectionable  because  in  nearly  all  cases  the  molecular 
equivalent  weights  represent  fractions  which  are  impossible  to  weigh 
without  an  accurate  analytical  balance.  For  example,  sodium 
acetate  1-351  gramme  would  require  (according  to  U.S.P.,  1890), 
