Am.  Jour.  Fnarir. 
January.  1903. 
Presence  of  Arse?iic  tn  Chemicals. 
35 
About  25  grammes  of  zinc  and  60  c.c.  (1  to  5)  of  sulphuric  acid 
were  used  for  each  operation.  That  is,  the  apparatus  was  thor- 
oughly cleaned  each  time  a  new  test  was  made. 
BettendorfT's  reagent  was  made  by  dissolving  pure  tin  foil  in  con- 
centrated hydrochloric  acid;  the  tin  was  added  until  the  solution  was 
thoroughly  saturated.  In  applying  this  reagent,  all  solutions  were 
highly  acidulated  with  hydrochloric  acid. 
Reinsch's  method  was  applied  in  the  usual  way,  no  special  precau- 
tions being  necessary,  except  when  organic  matter  was  present  or 
other  interfering  agents  were  indicated. 
A  careful  comparison  of  these  methods  with  known  material  gave 
the  following  results : 
Mg  of  As4Oe 
1. — i" 
-o*5 
3-— °25 
4-— 0T25 
Grains  of  As4Oe. 
1 '6= 
1  129 
.0-0154 
1/260  =OCO' 
Marsh-Berzelius. 
Color  black 
immediately. 
Color  black 
immediately. 
Color  black 
immediately. 
1/520  =0*00192  Color  lighter 
black  in  two 
minutes  than 
No.  3. 
Reinsch's. 
Foil  black  al- 
most instantly. 
Crystals  many 
and  large. 
Foil  black  al- 
most instantly. 
Crystals  many 
and  large. 
Foil  dark  gray. 
Crystals  large 
and.  many. 
Foil  dark  gray. 
Crystals  large 
and  many. 
Bettendorff's. 
C  o  n  s  i  d  erably 
less  gave  a  de- 
cided reaction. 
C  onsiderably 
less  gave  a  de- 
cided reaction. 
Tin-foil  and  so- 
lution colored 
within  two 
minutes.  Bad 
in  fifteen  min- 
utes. 
Not  so  intense 
a  coloration  as 
No.  3. 
5. — 0*0625     1/1037  -=0*00096  Color  lighter  Foil  much  col-  Solution  and 
black  in  five  ored,  crystals  tin  show  color- 
minutes  than  plain.  ation  within  fif- 
No.  3.  teen  minutes. 
-0*03125  1/2074  =0*00048  Color  lighter 
than  No.  5; 
time,  seven 
minutes. 
Foil 
dar! 
color.  Crystals 
plain. 
assumes 
purple 
Color  did  not 
show  up  within 
fifteen  minutes. 
After  twenty- 
five  minutes, 
slight  colora- 
tion of  tin-foil. 
)'0i562  1/4149 
:o*ooQ24  Color  lighter 
than  No.  6; 
time  ten  min- 
utes. 
Foil  slightly 
colored  purple. 
Crystals  plain. 
After  an  hour 
there  seemed  to 
be  a  slight  col- 
oration. 
