A^ug0ust,r8h94.rm"}    Report  of  Research  Committee  B.  389 
lumps.  There  could  be  a  distinction  made  between  the  firm  flocculi 
of  Sb  or  Bi  and  the  finely  divided  brown  particles  of  arsenic,  but  it 
would  hardly  be  safe  to  trust  to  this  appearance  for  a  sufficient  evi- 
dence of  the  presence  of  arsenic,  and  the  preparations  of  Bi  and  Sb 
must  be  tested  without  the  aid  of  metallic  tin. 
A  number  of  specimens  of  pure  bismuth  and  antimony  salts  were 
tested  with  the  U.  S.  P.  and  the  German  solution  of  stannous 
chlorid  in  various  proportions ;  but  neither  at  ordinary  tempera- 
ture, nor  when  heated,  did  the  least  coloring  occur. 
4.    INFLUENCE    OF    THE    PRESENCE    OF     OTHER    SUBSTANCES    IN  THE 
SPECIMEN  TESTED. 
The  preceding  experiments  were  made  with  a  solution  of  either 
arsenic  trioxid  or  sodium  arsenite  or  arsenate  in  water,  other  sub- 
stances being  absent.  But  in  testing  various  chemicals  for  traces  of 
arsenic  there  are  different  conditions,  as  the  arsenic  forms  only  a 
very  small  portion  of  the  mixture.  In  the  U.  S.  P.  the  Bettendorf 
test  is  directed  for  1 1  preparations  :  For  hydrobromic,  hydrochloric, 
phosphoric  and  sulphuric  acid,  1  cc.  of  the  acid  is  to  be  tested  by 
mixing  with  I  cc.  of  the  reagent,  adding  a  small  piece  of  tinfoil  and 
heating.  In  case  of  magnesium  sulfate,  I  gm.  of  the  dry  substance 
is  to  be  shaken  with  3  cc.  of  the  reagent,  metallic  tin  is  then  to  be 
added  and  an  hour  allowed  for  the  appearance  of  the  reaction ; 
sodium  phosphate  and  pyrophosphate  are  treated  in  like  manner, 
but  heat  applied  and  15  minutes'  time  given. 
In  the  case  of  antimony  and  potassium  tartrate,  antimony  oxid, 
bismuth  subcarbonate  and  bismuth  subnitrate,  it  was  intended  to 
test  with  stannous  chlorid  alone  for  an  hour,  but  by  an  unfortunate 
misunderstanding  of  the  transcriber,  tinfoil  was  directed  to  be  added, 
which  will  reduce  Bi  and  Sn  as  well  as  As. 
To  find  whether  any  of  the  chemicals  directed  to  be  tested  by  the 
stannous  chlorid  method  could  influence  the  detection  of  arsenic, 
specimens  were  prepared  containing  the  pure  chemicals,  shown  to 
be  free  from  arsenic  by  other  tests,  and  with  these  small  portions  of 
arsenic  were  mixed,  and  the  tests  compared  with  those  in  which 
arsenic  was  present  in  equal  amount  without  admixture  with  the 
chemicals. 
In  no  case  could  any  difference  in  the  intensity  of  the  test  be 
made  out,  nor  were  the  differences  in  the  time  of  the  occurrence  of 
