226 
Arsenic  Tribromide. 
(  Am.  Jour.  Pharm. 
1      May,  1883. 
arsenic.  AsBrg  is  not  volatile  at  ordinary  temperatures,  as  it  is  a  solid. 
The  conclusion  was  probably  drawn  from  having  an  excess  of  bromine 
in  solution.  Of  course  the  crystallized  compound  would  fume  in 
moist  air,  but  would  only  give  off  hydrobromic  acid  gas. 
The  striking  similarity  of  the  halogen  compounds  of  the  group  of 
metals  to  which  arsenic  belongs,  and  their  peculiar  decomposition  with 
water,  leads  us  at  once  to  infer  that  an  aqueous  solution  of  AsBrg  is  an 
impossibility. 
Wallace,  in  1859,^  showed  that  arsenious  anhydride  was  very  solu- 
ble in  melted  AsBr3 ;  that  one  part  AsBrg,  dissolved  in  three  parts 
boiling  water  and  allowed  to  cool,  gave  crystals  of  pure  arsenious 
anhydride ;  that  AsBrg  boiled  with  a  large  amount  of  water  contain- 
ing hydrobromic  acid,  an  insoluble  precipitate  was  formed ;  that  the 
same  was  arsenious  dibromide  (AsOBr) ;  that  if  AsBrg  was  dissolved 
in  cold  water  containing  a  large  amount  of  hydrobromic  acid,  and  the 
solution  allowed  to  evaporate  without  heating,  crystals  of  AsOBr-f 
SH^O  were  formed.  Further,  if  AsBrg  was  dissolved  in  a  similar 
strongly  acid  solution,  by  boiling,  and  evaporated  to  crystallization,  it 
gave  crystals  of  2AsOBr.3As203-|-(24H20).  Then  Nickles'  verified 
these  results  in  a  great  measure  by  his  parallel  researches  on  the  action 
of  water  on  Aslg.  Serullas^  conclusively  proved  that  AsBrg,  dissolved 
in  a  large  amount  of  water,  was  entirely  decomposed  into  arsenious 
anhydride  and  hydrobromic  acid,  and  when  dissolved  in  the  least  possi- 
ble amount  of  water  gave  AsOBr  and  hydrobromic  acid.  From  the 
above  we  see  that  the  solution  of  AsBrg,  as  prepared  by  Mr.  Fair- 
thorne,  is  nothing  but  a  weak  hydrobromic  acid  solution  of  arsenious 
anhydride,  and,  further,  that  an  aqueous  solution  of  AsBrg  is  impos- 
sible. 
The  question  is,  how  to  administer  AsBr,  as  such,  and  whether  it  is 
beneficial  to  introduce  such  a  strong  oxidizing  substance  into  the 
stcjmach.  Undoubtedly  not,  for  the  immediate  violent  chemical  reac- 
tion, which  must  follow  when  AsBrg  is  brought  in  contact  with  the 
liquids  of  the  stomach  or  the  tissues,  could  only  produce  a  strong  caus- 
tic action.  If  there  is  medicinal  virtue  in  the  haloid  compounds  of 
arsenic,  the  writer  believes  it  must  lie  in  the  oxy-compounds  AsOBr 
or  AsOI.    These  are  easily  prepared  by  the  methods  given  above,  and 
i"Phil.  Mag."  [4],  17,  p.  261. 
2 "  Jour.  Phar.  et  Chim."  [3],  36,  p.  161. 
"  Schw.  Jour./'  55,  p.  345. 
