ANo/e°mbe?hia9i7'  J    Dakin  or  Carrel-Dakin  Solution.  -499 
Pour  into  a  12-liter  bottle  the  chlorinated  lime  and  five  liters  of 
water,  shake  vigorously  for  a  few  minutes  and  allow  the  mixture 
to  stand  for  twelve  hours,  shaking  at  frequent  intervals.  Dissolve 
the  sodium  salts  in  five  liters  of  water  and  after  the  maceration  of 
the  chlorinated  lime  is  completed  pour  the  solution  of  the  sodium 
salts  into  the  other  mixture  and  mix  thoroughly.  Allow  the  mixture 
to  stand  for  at  least  a  half  hour  until  the  reaction  is  complete  and 
the  calcium  carbonate  has  subsided.  Siphon  off  the  supernatant 
liquid  and  filter  through  white  filter  paper.  The  solution  is  then 
ready  for  use. 
Titration  of  the  Chlorinated  Lime. — Because  of  the  varia- 
tion of  this  product  as  now  obtained  on  the  market,  it  is  necessary 
to  determine  the  amount  of  active  chlorine  contained  in  the  chlo- 
rinated lime  which  is  to  be  used.  This  is  done  in  order  to  use  an 
exact  calculated  quantity  according  to  its  concentration.  The  assay 
is  carried  on  in  the  following  manner : 
Take  from  different  parts  of  the  container  a  small  quantity  of 
the  chlorinated  lime  so  as  to  have  exactly  20  Gm.  of  a  representative 
sample ;  mix  it  as  thoroughly  as  possible  in  a  liter  of  water  and 
allow  the  mixture  to  stand  for  a  few  hours. 
Measure  10  mils  of  the  clear  supernatant  liquid  and  add  20  mils 
of  a  10  per  cent,  solution  of  potassium  iodide  and  2  mils  of  acetic  or 
hydrochloric  acid,  then  carefully  titrate  with  sodium  thiosul- 
phate  solution,  decoloration  of  course  denoting  the  end  reaction. 
The  number  of  mils  of  the  ^  sodium  thiosulphate  solution  used  mul- 
tiplied by  1.775  wnl  giye  the  weight  of  active  or  available  chlorine 
contained  in  100  Gm.  of  the  chlorinated  lime ;  in  other  words  the 
percentage  of  chlorine. 
This  assay  must  be  made  every  time  the  solution  is  being  pre- 
pared. When  the  result  obtained  differs  from  30  per  cent.,  it  will 
be  necessary  to  increase  or  reduce  the  proportion  of  the  three  ingre- 
dients in  the  formula.  This  can  be  easily  done  by  multiplying  each 
of  the  three  numbers  154,  77  and  64  by  the  factor  30/X  in  which  X 
is  the  per  cent,  of  active  chlorine  in  the  chlorinated  lime  used. 
Assay  of  the  Finished  Solution. — It  is  the  correct  policy  to 
assay  the  finished  product  as  well  and  this  is  done  in  the  following 
way : 
To  ten  mils  of  the  finished  solution  add  20  mils  of  10  per  cent, 
solution  of  potassium  iodide  and  2  mils  of  acetic  or  hydrochloric 
acid.    Titrate  with       sodium  thiosulphate  solution  until  decolora- 
