ANovembe?a896?'}  Antimonii  Oxidum  and  Pulvis  Antimonialis.  599 
The  pentoxide  or  antimonic  oxide,  Sb205,  does  not  exist  in 
nature,  but  is  prepared  artificially.  It  is  easily  distinguished  from 
the  trioxide  by  the  liberation  of  iodine,  which  takes  place  when 
potassium  iodide  is  added  to  a  solution  of  the  oxide  in  hydrochloric 
acid. 
The  so-called  tetroxide,  Sb204,  considered  by  some  authors  as 
antimonous  antimonate  Sb2(Sb04)2,  or  antimonyl  antimonate, 
(SbO)Sb03,  is  obtained  when  either  of  the  other  oxides  is  ignited 
with  access  of  air.  It  acts  in  some  respects  as  a  compound  contain- 
ing both  Sb203  and  Sb205 ;  but  while  it  liberates  iodine  from 
potassium  iodide  like  the  pentoxide,  it  does  not  resemble  the  tri- 
oxide by  precipitating  argentous  oxide.  Several  hydrated  com- 
pounds of  these  oxides  are  known,  their  formation  depending  upon 
the  method  of  precipitation  and  the  temperature  at  which  the  pre- 
cipitate is  dried. 
Three  different  methods  were  used  for  the  estimation  of 
the  antimony  in  the  samples'  of  oxide  examined  by  the  writer. 
No.  1  was  based  upon  the  following  equation :  4I  -J-  Sb2Oa  -f 
2H20  =  4HI  -f  Sb205.  This  method  served  for  the  estimation  of 
the  antimonous  oxide.  The  details  of  the  process  are  as  follows : 
a  weighed  quantity  of  the  oxide  (about  0  2  gm.)  is  warmed  with  an 
excess  of  tartaric  acid  solution  for  about  fifteen  minutes ;  the  excess 
of  acid  is  then  neutralized  with  sodium  carbonate,  and  a  saturated 
solution  of  sodium  bicarbonate  in  water  is  added,  in  the  proportion 
of  about  20  cubic  centimetres  to  each  01  gm.  of  Sb203  taken.  The 
liquid  is  then  titrated  with  decinormal  iodine  solution,  using  starch 
paste  as  an  indicator.  The  percentage  of  antimony  is  easily  calcu- 
lated from  the  amount  of  iodine  solution  used,  each  cubic  centi- 
metre of  the  latter  corresponding  to  -006  gramme  Sb. 
Method  No.  2  depended  upon  the  reducing  action  of  hydriodic 
acid  upon  antimonic  compounds,  SbG5  -f  5KI  =  Sbl3  -j-  2I  -j- 
5KCI,  hydrochloric  acid  being  present  in  the  solution.  It  was  used 
for  estimating  the  total  amount  of  Sb  present  by  first  heating  the 
sample  in  a  beaker  with  HC1  and  KC103,  whereby  antimonous  com- 
pounds are  oxidized  to  antimonic.  The  chlorine  is  then  driven  off 
by  heating  in  a  water-bath,  the  liquid  is  cooled  and  potassium  iodide 
is  added  in  excess.  The  iodine  liberated  is  estimated  by  titration 
with  decinormal  sodium  thiosulphate  solution,  the  results  being 
calculated  in  the  same  manner  as  those  in  the  previous  case. 
