3io  Ike  U.S.P.  Inorganic  Chemicals.  {Am,juiuyr;5£rm* 
slowly  and  unsatisfactorily  with  diluted  sulfuric  acid,  hence  the  sub- 
stitution of  hydrochloric  acid. 
The  limit  of  delicacy  of  this  test  may  be  placed  at  0.002  milli- 
gramme of  As203,  this  amount  produces  a  faint  but  distinct  yellow 
stain  upon  the  test-cap. 
Bettendotf  s  Test.  U.S.P. ,  ^<5<5.~The  test  as  recognized  in  the  last 
edition  of  the  Pharm.  Ger.,  consists  in  simply  adding  a  concentrated 
solution  of  the  chemical  to  be  tested  to  a  freshly  prepared  solution 
of  stannous  chlorid  in  concentrated  hydrochloric  acid.  The  em- 
ployment of  the  tinfoil,  as  directed  in  our  last  revision,  is  not 
advisable,  owing  to  its  tendency  to  cause  a  reduction  of  other 
metals,  producing  a  reaction  simulating  that  of  arsenic  (Paul  and 
Cownley,  Pharm.  Jour.  Trans.,  1893,  431,  and  Curtman,  Pharm. 
Rundschau,  1894,  15.) 
To  obtain  a  clear  solution  of  the  reagent  which  will  remain  clear 
and  colorless  on  warming  and  respond  readily  to  the  presence  of 
arsenic,  it  is  absolutely  necessary  that  the  stannous  chlorid  be 
freshly  prepared.  Commercial  stannous  chlorid  yields  a  yellow  to 
brownish  solution  when  warmed  with  hydrochloric  acid. 
The  chief  objections  that  have  been  offered  to  this  test  are: 
(a)  Fails  to  give  evidence  with  less  than  0*1  milligramme  As203 
in  I  c.c.  The  presence  of  mercury,  tellurium  and  selenium  (fre- 
quently occurring  in  acids),  which  produce  reactions  simulating 
those  of  arsenic.    (Dawydon,  Ch.  Zeitg.,  1895,  P-  7°-) 
(b)  Liability  of  error,  due  to  deterioration  of  the  stannous  chlorid 
(Geissler,  Phatm.  Centh.,  1895,  P-  59 
The  advantages  claimed  for  this  reagent  are  its  simplicity  of 
application  and  adaptability  to  the  detection  of  arsenic  in  the  presence 
of  antimony.  As  to  delicacy  of  reaction,  Beckurts  (Beckurts,  Pharm. 
Centh.,  1891,  p.  570)  gives  o-i  milligramme  as  the  limit,  Frerichs 
(Frerichs,  Apoth.  Ztg.y  1897,  p.  176)  claims  to  be  able  to  identify 
3^  milligramme  of  arsenous  oxide  in  one  hour's  time. 
Curtman  places  the  limit  at  o-i  milligramme,  and  states  that 
if  after  one  hour's  time  no  reaction  takes  place,  then  less  than  T^ 
per  cent,  of  As203  may  be  present. 
We  have  found  that  0  02  milligramme  will  produce  a  very  faint 
brownish  tint  when  viewed  by  reflected  light  on  a  white  surface. 
Comparison  should  always  be  made  with  a  solution  of  the  reagent 
under  the  same  conditions.  Sulfates  and  sulfids  should  be  absent 
from  the  chemicals  being  tested. 
