350 
ON  THE  VALUATION  OF  CHLORIDE  OF  LIME. 
take  an  average  specimen  of  chloride  of  lime,  and  weigh  out 
100  grains  of  it,  and  make  in  the  usual  way  a  solution  of  it  by 
trituration  in  a  mortar  with  some  water;  pour  it  into  the  flask 
which  was  used  in  preparing  the  two  standard  solutions,  and 
having  filled  up  with  water  to  the  mark  in  the  neck,  mix  the 
solution  thoroughly ;  and  before  each  time  that  any  of  the 
chloride  of  lime  is  taken  out,  shake  well  the  contents  of  the 
flask. 
Measure  out  into  a  beaker-glass,  by  means  of  the  two  little 
bottles,  100  divisions  of  the  chloride  of  lime  solution,  and  50  of 
the  standard  solution  of  ferrocyanide  ;  end  having  mixed  them 
well  together,  add  some  hydrochloric  acid  to  dissolve  the  pre- 
cipitate formed  and  acidify  the  mixture  strongly;  and  having 
mixed  the  whole  well,  pour  from  the  burette  slowly  the  standard 
solution  of  bichromate  (stirring  well  all  the  while)  till  a  drop 
taken  from  the  mixture  and  brought  in  contact  with  a  drop  of  a 
very  weak  solution  of  perchloride  of  iron  produces  a  yellowish- 
brown  color,  as  already  noticed.  Then  read  off  the  number  of 
divisions  of  the  standard  solution  of  bichromate  which  was 
necessary  to  produce  this  effect ;  and  this  being  deducted  from 
50,  gives  the  per-centage  by  weight  of  chlorine. 
For  the  standard  solution  of  ferrocyanide  having  been  made 
so  that  the  10,000  grain  measure  should  be  equivalent  to  100 
grains  of  chlorine,  and  as  every  division  of  the  burette  equals 
10  grains,  each  of  these  divisions  of  the  ferrocyanide  solution 
converted  into  ferridcyanide  will  indicate  0*1  grain  of  chlorine. 
Again,  the  100  divisions  of  the  solution  of  chloride  of  lime 
represent  10  grains  of  that  substance,  and  we  want  to  know 
how  many  divisions  of  the  ferrocyanide  solution  its  chlorine  has 
converted  into  ferridcyanide.  This  is  readily  ascertained  by 
the  bichromate  solution,  which  has  been  so  graduated  that  each 
division  represents  a  division  of  the  ferrocyanide  solution.  So 
that  to  determine  the  per-centage  of  chlorine  we  have  only  to 
deduct,  as  before  stated,  the  number  of  divisions  of  the  bichro- 
mate solution  employed  from  the  50  of  the  ferrocyanide  solution, 
and  the  diff*erence  gives  us  the  per-centage  of  chlorine  by  weight 
in  the  sample ;  thus  in  four  experiments  50  divisions  of  the 
ferrocyanide  solution  mixed  with  100  divisions  of  the  solution 
of  chloride  of  lime,  required  18-5  divisions  of  the  bichromate 
