AnAuJS^m'}    Report  of  Research  Committee  B.  385 
A  number  of  specimens  of  arsenic  solution  were  made,  contain- 
ing free  trioxid,  sodium  metarsenite  and  sodium  arsenate,  in  such 
proportion  that  each  set  corresponded  exactly  to  an  equal  amount 
of  As.  They  were:  Arsenic  trioxid  (As203  ==  197-68),  of  which 
1-31962  gm.  contain  1  gm.  of  As. 
Sodium  metarsenite  (NaAs02  =  128-82),  of  which  17332  gm. 
contain  1  gm.  of  As. 
Sodium  arsenate,  U.  S.  P.  (Na2KAs04  -f  7  H20  —  311-46),  of 
which  4-51834  gm.  contain  I  gm.  of  As. 
The  solutions  used  for  experiments  contained  from  0-5  gm.  to 
o  01  gm.  of  As. 
Of  these  1  cc.  was  used  for  each  trial  and  the  amount  of  reagent 
mixed  with  this  varied  frpm  1  cc.  to  3  cc.  so  as  to  correspond  with 
the  limits  prescribed  in  the  pharmacopceial  tests.  When  metallic 
tin  was  added  to  the  reagent,  1  cc.  each  of  the  specimen  and  the 
stannous  chlorid  solution  was  used.  In  some  cases  of  doubt  a  ten- 
fold quantity  (10  :  30  cc,  etc.)  was  used,  to  obtain  sufficient  material 
for  colorimetric  comparison. 
A  uniform  application  of  heat  was  effected,  whenever  needed,  by 
imbedding  the  series  of  test  tubes  under  observation  to  an  equal 
depth,  into  a  sand-bath,  heated  to  about  8o°  C. 
Whenever  comparisons  of  color  became  necessary  to  decide 
whether  a  deeper  color  had  been  produced  than  that  of  the  unaffected 
reagent  (as  was  especially  necessary  with  the  yellowish  solution  of 
the  German  Pharmacopoeia),  or  whether  a  greater  or  less  intensity 
cf  color  characterized  the  reaction,  narrow  graduated  cylinders,  of 
10  cc.  capacity,  were  used  in  a  dark  box,  with  light  reflected  from 
beneath,  or  occasionally,  for  still  greater  accuracy,  a  pair  of  Hehner's 
colorimeter  cylinders  of  100  cc.  capacity,  also  placed  for  observation 
into  a  dark  box,  admitting  from  beneath  light  reflected  upward  by 
a  plate  of  milk  glass,  placed  at  an  angle  of  45  °. 
With,  the  aid  of  these  appliances  the  following  results  were 
obtained : 
(a)  With  the  U.  S.  P.  solution  of  stannous  chlorid,  of  specific 
gravity  1-467,  1  cc.  of  each  Of  the  three  specimens,  containing  0-5 
mgm.  of  As  was  mixed  in  the  different  proportions  stated  below 
and  kept  at  ordinary  temperature  for  one  hour. 
With  1  cc.  of  reagent  a  sharp  reaction  had  taken  place  at  the 
end  of  the  hour. 
