62 
ON  CHLORIMETRY. 
Notwithstanding  many  advantages,  this  method  has  met  with 
but  little  acceptance,  probably  because  sulphurous  acid  is  not 
much  employed  in  chemical  laboratories ;  and,  moreover,  the 
aqueous  solutions  both  of  the  free  acid  and  its  salts  are  converted 
by  keeping  into  sulphuric  acid  and  sulphates,  so  that  when  chlori- 
metric  investigations  only  occur  at  considerable  intervals,  it  is 
necessary  to  prepare  this  substance  afresh  upon  each  occasion, 
which  will,  of  course,  render  the  whole  operation  much  too  long 
for  many. 
All  these  disadvantages  are  got  rid  of  by  employing,  instead 
of  sulphurous  acid,  hyposulphite  of  soda,  which  is  also  converted 
into  sulphate  by  free  chlorine  even  at  ordinary  temperatures,  and 
has  hence  been  long  employed  for  the  removal  of  the  last  traces 
of  chlorine  from  the  stuffs  bleached  by  it. 
1  grm.  of  a  sample  of  chloride  of  lime  is  mixed  with  about  2 
grms.  of  hyposulphite  of  soda  and  water  in  a  flask  of  such  size, 
that  wThen  closed  with  a  cork  there  shall  be  room  enough  left  to 
allow  of  the  complete  diffusion  of  the  chloride  of  lime  by  shaking, 
which  is  usually  effected  with  ease.  The  complete  conversion  of 
the  hyposulphite  into  sulphate  takes  place  even  in  the  cold,  but 
for  greater  certainty  the  flask  is  heated  a  little  in  the  water-bath. 
It  is  then  mixed  with  a  few  drops  of  pure  muriatic  acid,  or  rather 
a  sufficient  quantity  to  make  sure  of  the  decomposition  of  all  the 
excess  of  hyposulphite  of  soda,  which  takes  place  in  the  heated 
fluid  immediately,  with  formation  of  sulphurous  acid  and  sulphur. 
By  inclining  the  flask  and  boiling  for  a  few  minutes,  all  the  sul- 
phurous acid  is  expelled,  and  the  sulphur  is  deposited  in  drops 
exactly  as  in  the  decomposition  of  the  metallic  sulphurets  by 
aoids ;  so  that  on  the  complete  decomposition  of  the  excess  of 
hyposulphite  of  soda,  the  fluid,  which  was  at  first  milky  and 
yellowish-white,  becomes  nearly  limpid,  and  its  separation  from 
the  melted  sulphur  by  filtration  is  very  easily  effected,  as  is  also 
the  subsequent  washing  of  the  filter.  The  filtrate  then  contains 
the  chloride  of  calcium  of  the  chloride  of  lime,  the  excess  of  the 
muriatic  acid  added,  and  the  chloride  of  sodium  produced,  to- 
gether with  a  quantity  of  sulphate  of  soda  exactly  corresponding 
with  the  amount  of  oxidizing  chlorine.  This  is  precipitated  with 
muriate  of  baryta. 
As  16  of  sulphur  take  up  8  of  oxygen  to  form  Lyposulphurous 
