386  Report  of  Research  Committee  B.  {^•^•>SSirm- 
With  2  cc.  of  reagent  the  reaction  was  obtained  earlier  and  was 
more  intense  at  the  end  of  one  hour. 
With  3  cc.  of  the  reagent,  the  reaction  was  still  more  speedy,  and 
at  the  end  of  the  hour  more  intense. 
No  difference  could  be  noticed  either  in  time  or  in  intensity 
between  arsenic  in  the  state  of  trioxid  or  pentoxid. 
When  the  test  tubes  were  arranged  exactly  as  before,  but  placed 
in  hot  sand,  the  time  was  somewhat  shortened,  and  a  slight  increase 
of  intensity  noticed  in  all  of  the  specimens. 
(U)  When  I  cc.  of  the  U.  S.  P.  solution  was  used  with  I  cc.  of 
solutions  containing  0.5  mgm.  of  As  and  a  small  piece  of  metallic 
tin  added,  and  heat  applied,  the  reaction  was  almost  instantaneous, 
and  in  3  minutes  very  sharp,  unmistakable  coloration  appeared, 
which  continued  to  increase  in  intensity  for  about  10  or  15  minutes, 
but  was  not  notably  darker  at  the  end  of  the  hour.  No  difference 
appeared  in  the  different  solutions  containing  arsenite  or  arsenate. 
(c)  When  from  1  to  3  cc.  of  the  stannous  chlorid  solution  of  the 
German  pharmacopoeia  was  used  with  I  cc.  of  the  solutions  containing 
0  5  mgm.  of  As,  there  was  a  slight  darkening  of  the  color  in  a  few 
minutes,  which  continued  to  increase  to  the  end  of  the  hour.  No 
difference  was  perceivable  between  the  arsenious  and  the  arsenic 
preparations.  At  15  minutes,  the  specimens  treated  by  U.  S.  P. 
solution  and  metallic  tin  showed  a  much  greater  intensity  of  color, 
but  toward  the  end  of  the  hour  there  was  but  little  difference  per- 
ceptible between  the  color  of  the  specimens  treated  with  3  cc.  of  the 
German  reagent,  without  heat,  and  that  treated  with  1  cc.  of  the 
U.  S.  P.  reagent,  metallic  tin  and  heat.  The  specimens  containing 
less  than  2-5  cc.  of  reagent  showed  a  less  intense  color. 
These  experiments  were  repeated  with  the  three  solutions  con- 
taining 0  05  mgm.  As  in  1  cc.  and  resulted  as  follows : 
(a)  With  the  U.  S.  P.  solution  of  SnCl2 : 
1  cc.  of  reagent  gave  no  reaction  during  45  minutes;  then  grad- 
ual coloration  began.  If  heat  be  applied  the  reaction  begins  in  18 
minutes,  and  at  the  end  of  one  hour  is  slightly  more  intense  than 
when  treated  without  heat. 
1-5  cc.  of  reagent:  reaction  slightly  more  rapid  and  intense  than 
with  i  cc. 
2  0  cc.  of  reagent :  still  more  rapid  and  intense,  both  with  or 
without  heating. 
