5/6  Determining  the  Water  in  Iodine.  {^sS^SS^0' 
perature.  The  concentration  of  the  solution  of  the  halogen  salts  of 
the  alkalies  has  also  a  marked  effect  on  the  solubility  of  the  silver 
compounds  ;  a  10  per  cent,  solution  of  sodium  chloride  and  a  I  per 
cent,  solution  of  potassium  iodide  dissolving  scarcely  any  recogniz- 
able quantity  of  the  corresponding  silver  compounds.  The  very 
great  difference  between  chlorine  and  iodine  is  shown  both  in  the 
relative  solubility  of  silver  chloride  and  silver  iodide,  and  in  the  dif- 
ferent solvent  power  of  the  halogen  alkali  salts  on  silver  nitrate, 
silver  chloride,  etc. ;  bromine  occupying  a  position  between  chlorine 
and  iodine.  For  example,  100  grams  of  sodium  chloride  or  of  potas- 
sium chloride  in  a  20  per  cent,  solution  dissolves  hardly  a  trace  of 
silver  iodide,  whilst  100  grams  of  potassium  iodide  in  concentrated 
solution  dissolves  about  90  grams  of  the  salt,  and  a  boiling  saturated 
solution  dissolves  4-5  times  that  quantity.  Mixtures  of  the  halogen 
saltsof  the  alkalies,  in  particular  proportions,  are  unable  to  dissolve 
as  much  of  the  silver  salt  as  each  can  before  admixture. 
A  SIMPLE  METHOD  FOR  DETERMINING  THE  WATER 
IN  IODINE. 
By  Prof.  Dr.  Meixcke. 
For  determining  the  water  01  crystallization  in  iodiferous  sub- 
stances readily  capable  of  decomposition,  E.  Ostermeyer  passes  the 
vapors  of  iodine  and  water,  by  means  of  a  current  of  air,  through  a 
moderately  heated  combustion  tube  filled  with  spirals  of  sheet 
silver  or  copper,  and  allows  the  watery  vapors,  freed  from  iodine,  to 
be  absorbed  in  weighed  drying  tubes.  When  it  is  merely  required 
to  determine  relatively  small  quantities  of  iodine,  the  metal  spirals 
do  good  service  ;  but  as  the  proportion  of  moisture  in  iodine  is 
generally  small,  it  is  desirable  to  take  for  its  determination  not  too 
small  a  quantity  of  the  material.  Hence  the  danger  that  the  iodine 
may  escape  absorption  by  the  spirals  is  increased,  except  they  are 
made  of  an  inconvenient  length. 
My  procedure,  in  which  this  risk  is  not  merely  obviated,  but  the 
apparatus  is  of  the  utmost  simplicity,  is  as  follows  : 
The  iodine  to  be  examined  is  allowed  to  fall  from  the  weighing- 
glass  into  a  test-tube  of  about  1  cm.  in  width  and  6  cm.  in  length  ; 
it  is  at  once  superstratified  with  from  four  to  five  times  its  quantity 
of  silver  powder,  previously  ignited  ;  the  tube  is  closed  with  a  glass 
'stopper,  ground  to  tit  its  mouth,  and  weighed  immediate!}' ;  or,  if 
