ADeciXrPbifoT'}      Inorganic  Chemistry  of  the  US. P.  555 
readily  upon  exposure,  disengaging  chlorine.  It  is  this  chlorine,  the 
"  available  chlorine,"  to  which  the  preparation  owes  its  value  as  a 
bleaching  and  disinfecting  agent. 
The  composition  of  chlorinated  lime  is  most  frequently  expressed 
CaCl2  +  Ca(C10)2. 
The  Pharmacopoeia  of  1880  required  it  to  contain  25  per  cent,  of 
available  chlorine,  that  of  1890  35  per  cent.,  the  present  Pharma- 
copoeia requires  30  per  cent.,  which  is  more  nearly  the  quantity 
found  in  commercial  samples.  Theoretically  it  should  contain  about 
39  per  cent.  This  preparation  is  also  official  in  the  German  Phar- 
macopoeia under  the  name  of  Calcarea  Chlorata)  and  is  required  to 
contain  25  per  cent,  of  available  chlorine. 
The  assay  process  for  available  chlorine,  as  given  in  the  U.S.P., 
depends  upon  liberating  the  chlorine  by  the  addition  of  hydrochloric 
acid,  then  by  the  introduction  of  potassium  iodide,  taking  up  the 
chlorine  and  liberating  an  equivalent  of  iodine,  which  is  titrated 
with  one-tenth  normal  sodium  thiosulphate  V.  S.  The  quantity  of 
the  latter  consumed  multiplied  by  the  factor  for  chlorine,  0003518 
gramme,  gives  quantity  of  chlorine  present.  The  assay  process 
differs  from  that  of  the  previous  Pharmacopoeia  in  that  a  larger 
quantity  of  the  chlorinated  lime  is  taken  and  considerable  more 
water  used.  Thus  more  complete  solution  is  attained.  A  definite 
quantity  of  this  mixture  is  taken  for  analysis.  The  insoluble  lime 
residue  undoubtedly  interfered  with  the  attaining  of  correct  results 
in  the  old  method,  which  were  uniformly  too  low.  The  new  method 
is  a  better  one,  but  might  be  improved  by  directing  that  the  quantity 
of  solution  taken  for  analysis  be  decanted  from  the  sediment,  instead 
of  that  the  mixture  be  shaken,  and  then  100  c.c.  taken  for  analysis. 
Starch  is  not  used  as  an  indicator. 
Argenti  Nitras  Mitigatus  is  the  Argenti  nitras  dilutus  of  the  Phar- 
macopoeia of  1890,  and  Argenti  et  potassii  nitras  of  the  British 
Pharmacopoeia.  It  should  contain  not  less  than  33.3  per  cent,  of 
silver  nitrate.    In  the  1880  Pharmacopoeia  it  contained  50  per  cent. 
Potassa  is  now  more  properly  called  Potassii  Hydroxidum. — For 
over  half  a  century  it  has  been  officially  called  potassa.  Strictly 
speaking,  potassa  is  K20  as  soda  is  Na20,  whilst  the  substance 
which  has  so  long  borne  this  name  is  an  hydroxide. 
The  official  Potassii  hydroxidum  should  contain  85  per  cent,  of 
pure  anhydrous  potassium  hydroxide  and  not  more  than  2  per  cent. 
