4 1  8  Constitution  of  Bleaching  Powder,      { ^'^■<i^^':^^l''^' 
ent  in  bleaching  powder,  but  he  denies  any  chemical  combination  of  it 
with  CaOCl.  He  strongly  objects  to  considering  the  latter  as  com- 
posed according  to  Balard's  theory,  his  principal  argument  being  that 
on  distillation  with  strong  acids  it  does  not  yield  hypochlorous  acid,  but 
only  free  chlorine.  Goepner  distinguishes  the  one  from  the  other  by 
shaking  the  distillate  with  mercury,  which  with  CI  gives  a  white  pre- 
cipitate, but  with  CIO  a  brown  precipitate.  The  latter  Goepner  pro- 
fesses never  to  have  obtained,  but  he  is  contradicted  upon  this  point  by 
Schorlemmer,  who,  however,  leaves  untouched  the  argument  which 
Goepner  shares  with  Kolb,  viz.,  that  COg  never  evolves  from  dry 
bleaching  powder  anything  but  CI.  Goepner  further  maintains  that 
the  peculiar  smell  of  bleaching  powder  is  in  reality  only  that  of  very 
diluted  chlorine,  and  that  it  can  be  exactly  imitated  by  letting  a  drop 
of  chlorine  water  fall  into  a  half-gallon  bottle  full  of  air. 
The  newest  paper  upon  this  subject  (just  published)  is  by  Richters 
and  Juncker  ("  Dingler's  Journal,"  vol.  ccxi,  p.  31).  Whilst  contra- 
dicting both  Kolb  and  Goepner  on  several  points,  they  come  to  the 
same  conclusion  as  to  the  constitution  of  bleaching  powder,  viz.,  that 
the  assumption  of  the  existence  of  calcium  hypochlorite  in  dry  bleach- 
ing powder  is  untenable,  and  that  there  must  be  a  ternary  compound 
CaOCl  (or  CaOClo,  new  notation),  about  whose  internal  constitution 
nothing  is  at  yet  known.  R.  and  J.  maintain  that  CO2  has  no  per- 
ceptible action  at  all  upon  dry  bleaching  powder,  and  that  from  damp 
bleach  it  evolves  both  CI,  and  CIO.  They  also  found  that  accord- 
ing to  the  mode  of  manipulation  the  action  of  strong  acids  upon  bleach 
will  either  yield  only  CI,  or  only  CIO,  or  both,  but  the  question  can  be 
better  approached  by  using  phosphoric  acid,  which  does  not  act  upon 
calcium  chloride,  and  yet  evolves  from  bleach  (upon  distillation)  only 
chlorine.  They  reject  mercury  as  a  reagent  for  the  distinction  between 
chlorine  and  hypochlorous  acid,  as  leading  too  easily  to  wrong  conclu- 
sions ;  instead  of  this  they  proceed  by  titrating  20  c.c.  of  the  distillate 
with  arsenious  acid,  and  another  20  c.c.  with  silver  nitrate,  after  neu- 
tralizing it  with  ammonia  and  evaporating  to  dryness.  They  give  the 
following  equations  : 
ClO+AsOg+HO^AsO^+HCl. 
2Cl+As03+2HO=As05+2HCl. 
The  same  amount  of  arsenious  acid,  therefore,  corresponds  to  one  HCl, 
and  one  AgONOg  for  hypochlorous  acid,  but  to   2HCI  and  two 
AgONOg  for  free  chlorine,  and  in  fact  it  is  found  that  the  distillate 
