Am•Julyr;l9oh6arm•}      The  U.S.P.  Inorganic  Chemicals.  307 
oxid  in  10,000.  While  this  may  suffice  for  all  chemicals  which  are 
given  in  moderate  doses,  yet  there  are  instances  in  which  it  is  evi- 
dently excessive,  as,  for  example,  such  salts  as  sodium  phosphate, 
sodium  sulfate,  acetates,  also  sulfur,  which  are  usually  given  in  large 
doses,  frequently  extending  over  considerable  periods  of  time. 
With  the  limit  set  at  yjtq  per  cent.,  or  one  part  in  10,000,  in 
each  ounce  of  these  chemicals,  about  3  milligrammes,  or  ^  of  a 
grain,  of  arsenous  acid  would  be  permissible,  and  considering  that 
some  of  these  are  given  in  doses  of  from  y2  to  2  ounces,  frequently 
repeated,  it  is  apparent  that  this  limit  is  too  low. 
Berzelius- Marsh  Test. — This  test,  originally  devised  by  Dr.  Marsh, 
who  directed  that  a  cold  porcelain  surface  be  held  over  the  burning  jet 
of  hydrogen,was  modified  and  improved  by  Berzelius,  in  directing  the 
heating  of  the  tube  through  which  the  arsine  gas  passed,  for  the  pro- 
duction of  the  well-known  metallic  mirror.  The  chief  difficulties  en- 
countered in  this  test,  as  well  as  all  others  based  on  the  generation  of 
arsine,  has  been  in  securing  samples  of  zinc  sufficiently  pure  and  free 
from  arsenic,  sulfur,  phosphorus  and  iron.  At  present  very  pure 
samples  of  zinc  are  readily  attainable  at  a  moderate  cost.  Such  zincs 
contain  only  traces  of  iron,  larger  quantities  interfere  seriously  with 
the  test,  since  iron  tends  to  form  an  insoluble  and  undecomposable 
arsenid.  Other  criticisms  which  have  been  made  of  this  well-known 
test  have  been  met  in  the  form  of  apparatus  and  procedure,  so 
accurately  described,  even  to  the  minutest  details,  by  the  Joint 
Committee  Report  of  the  Society  of  Chemical  Industry  and  the 
Society  of  Public  Analysts  (Jour.  Soc.  Chem.  Ind.y  1902,  p.  94). 
This  test  as  recommended  will  indicate  the  presence  of  1  part  of 
arsenous  oxide  in  7,000,000,  representing  yq^-q-q  of  a  grain  per 
pound  or  yi^-  of  a  grain  in  one  gallon  of  fluids.  O.  Hehner  states 
that  0  00 1  milligramme  of  As203  will  give  a  distinct  mirror  in  the 
tube,  in  1 5  minutes,  and  this  when  heated,  forms  crystals  of  As2Os, 
which  are  distinguishable  with  the  naked  eye. 
The  presence  of  quantities  of  selenous  acid  has  been  found  to 
interfere  with  the  formation  of  the  mirror.  This  test  is  too  sensi- 
tive for  general  and  pharmacopceial  purposes. 
Gutzeifs  Silver  Test,  U.S.P.  (18 go). — The  delicacy  of  this  test  is 
such  that  O  OOI  milligramme  of  As2Os  will  give  a  faint  yellow  spot 
which  turns  brown  on  wetting,  after  having  exposed  the  paper  cap, 
moistened  with  silver  nitrate,  to  the  action  of  mixed  hydrogen  and 
