AmjJuOiy'i906frm'}      The  U.S. P.  Inorganic  Chemicals.  305 
9  95  c.c.  of  N/i  H2S04,  or  0  6755  gramme,  9.95  c.c.  of  N/i  H2S04 
corresponding  to  a  99- 5  per  cent.  salt.  If,  on  the  other  hand,  an 
even  weight,  as  1  gramme  of  the  salt  (U.S.P.,  8th  Rev.),  which  can 
be  weighed  with  accuracy  upon  a  prescription  balan.ee,  be  taken, 
we  are  confronted  with  the  difficulty  of  measuring  fractions  of  a  cubic 
centimeter.  Thus  1  gramme  of  sodium  acetate  (99  5  per  cent.) 
should  require  14*74  c-c-  of  N/2  sulfuric  acid.  Since  1  c.c.  pipettes 
(graduated  to  hundredths)  are  cheaper  than  analytical  balances,  such 
fractions  of  a  cubic  centimeter  can  if  desired  be  measured,  otherwise 
the  nearest  whole  number  may  be  accepted.  The  pharmacopceial 
text  must  be  accurate  and  express  its  standards  accordingly,  the 
operator  may  interpret  to  suit  the  case  in  question. 
(8)  Time  Limit  Test  for  Metals. — Referring  to  the  old  sulfureted 
hydrogen  test  for  the  presence  of  undesirable  metallic  impurities, 
criticisms  have  frequently  been  made  of  the  lack  of  uniformity  in 
the  description  and  method  of  application  as  given  in  the  text  of 
the  last  revision. 
It  has  Been  further  noted  that  contrary  to  analytic  procedure, 
neither  time  nor  temperature  were  considered  in  applying  this  test  for 
the  presence  of  traces  of  metals,  precautions  which  are  especially 
necessary  in  testing  for  arsenic,  which  when  present  in  the  "  ic  " 
condition  must  first  undergo  reduction  to  the  "  ous  "  state,  before 
any  reaction  can  take  place.  It  was  decided  to  substitute  for  this 
the  "  time-limit  test  for  the  presence  of  poisonous  or  undesirable 
metallic  impurities."  The  limit  in  this  test  is  intended  to  be  about  1 
part  in  100,000. 
"A  solution  of  the  salt  or  acid  in  distilled  water  (1  in  20),  when 
the  former  is  slightly  acidulated  with  an  acid,  should  not  be  colored 
or  rendered  turbid  by  an  equal  volume  of  freshly  prepared  hydrogen 
sulphide  T.  S.,  alter  standing  well-stoppered  in  a  warm  place  for  at 
least  half  an  hour,  either  before  or  after  the  addition  of  ammonia 
water  to  slight  alkalinity."  After  the  lapse  of  one-half  hour  and 
before  the  addition  of  the  ammonia  water,  the  mixture  should  pos- 
sess the  distinct  odor  of  H2S,  if  not,  it  should  be  thoroughly  satu- 
rated with  the  gas  and  again  set  aside  for  half  an  hour. 
(9)  Special  Tests  for  Arsenic. — The  last  revision  recognized  five 
different  tests  for  the  presence  of  arsenic  ;  of  these  but  two  were 
employed  in  the  text  proper,  namely,  the  sulfureted  hydrogen 
and   Bettendorf's,  while  the  Fleitman,  Fleitman-Gatehouse  and 
