"^""-sllT^fjt'"' }      Conftitution  of  Bleaching  Powder.  4 1 7 
last  few  years  several  valuable  papers  have  been  published  by  chemists 
who  combine  practical  knowledge  of  the  manufacture  of  bleaching 
powder  with  that  of  scientific  chemistry,  and  they  nearly  all  seem  to 
agree  that,  whilst  the  product  of  the  action  of  water  upon  bleaching 
powder,  as  well  as  the  so-called  "  bleach  liquor,"  contains  a  mixture 
of  calcium  hypochlorite  and  calcium  chloride,  yet  in  the  dry  bleaching 
powder  the  calcium  hypochlorite  does  not  seem  to  exist.  I  do  not  here 
take  into  account  the  paper  Comptes  Rendus,"  vol.  Ixxiv,  p.  141 1) 
published  by  Grace  Calvert  in  1872  (giving  the  formula  CaOClOHri 
CaCl),  because  Kolb  has  shown  his  analytical  method  to  be  entirely 
fallacious,  and  even  theoretically,  Calvert  seems  to  have  made  a  grave 
omission,  since  3CaO  and  3CI  (old  equivalents)  do  not  exactly  give 
CaOC10+2CaCl,  but  leaves  an  O  to  spare,  which  is  not  in  any  way 
accounted  for. 
Kolb  (in  the  "  Bulletin  de  la  Societe  Chimique  "  for  1868,  ix,  p. 
82)  showed  that  dry  carbonic  acid  acts  upon  dry  bleaching  powder  in 
such  a  manner  that,  besides  calcium  carbonate,  only  free  chlorine,  and 
no  hypochlorous  acid,  is  generated  ;  he,  therefore,  rejected  the  formula 
of  Balard,  and  returned  to  CaOCl  (CaOClg,  new  equivalents),  his  ex- 
act formula  being  2(CaOClHO)-[-CaOHO-  In  damp  air,  however, 
bleaching  powder  yielded  to  him  hypochlorous  acid.  Bobierre  {Ibidem^ 
p.  172),  and  Scheurer-Kestner  [Ibidem^^.  159),  did  not  contradict  Kolb 
upon  this  point,  but  they  showed,  in  opposition  to  him,  that  if  the  tem- 
perature be  raised  too  much,  chlorine  acts  upon  calcium  hydrate  so  as 
partly  to  set  free  the  water  of  hydration,  and  they  both  show  (what  is 
known  to  all  practical  men)  that  if  a  great  excess  of  chlorine  acts 
upon  strong  bleaching  powder  the  available  chlorine  in  the  product  is 
actually  reduced.  In  1873,  Goepner  published  a  long  memoir  on 
bleaching  powder  ("  Dingler's  Journal,"  vol.  ccxxxix,  p.  204).  He 
showed  that  the  well-known  fact  of  calcium  chloride  being  always  present 
in  bleaching  powder  over  and  above  that  demanded  by  the  formula 
CaOC10-|-CaCl,  is  caused  by  the  presence  of  calcium  carbonate  in 
the  lime  employed  for  absorption,  either  from  imperfect  burning,  or  re- 
carbonation  of  the  same,  or  from  carbonates  present  in  the  manganese, 
the  action  of  chlorine  upon  calcium  carbonate  being  represented  by  the 
equation:  CaOC02+2Cl=C10+CaC14-C02.  In  his  opinion  this 
calcium  chloride  forms  a  wall  which  protects  a  portion  of  the  calcium 
hydrate  from  the  action  of  chlorine,  and  thus  he  explains  the  long- 
established  fact  that  there  is  always  a  quantity  of  calcium  hydrate  pres- 
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