AmNov.^i8^arm'}-^7to-s"^w  Ferrocyanide  and  Ferricyanide.  S77 
in  case  of  a  high  temperature  of  the  air,  the  silver  is  being  attacked 
by  the  iodine  on  mutual  contact,  not  until  completely  cold.  The 
open  tube,  which  may  be  set  in  a  small  beaker,  is  heated  upon  an 
asbestos  plate,  so  gently  that  only  a  very  slow  formation  of  silver 
iodide  takes  place.  As  this  reaction  can  always  be  observed,  it 
may  be  easily  regulated  in  case  of  need  by  removing  the  beaker 
from  the  asbestos  plate.  With  experience,  which  is  easily  acquired, 
there  is  no  risk  of  the  escape  of  even  traces  of  iodine.  Should  it 
really  occur,  it  would  be  inevitably  shown  by  a  change  of  the  color 
of  the  silver  powder;  the  silver  powder  then  appears  attacked  to  its 
upper  layer,  whilst  if  the  operation  is  correctly  managed,  the  upper 
portions  of  the  silver  must  remain  unchanged.  During  the  forma- 
tion of  silver  iodide,  the  water  which  escapes  is  condensed  in  the 
colder  parts  of  the  tube,  from  which,  after  the  complete  absorption 
of  the  iodine,  it  is  expelled  by  a  higher  temperature.  When  this 
takes  place,  the  tube  is  stoppered  up,  allowed  to  cool,  and  weighed. 
The  difference  shows  the  quantity  of  water  which  has  been  present 
in  the  iodine.  The  determination,  with  all  the  preparations,  scarcely 
requires  one  hour. 
The  method  allows  of  an  accurate  determination  of  moisture  in 
iodine,  even  if  chlorine  and  bromine  are  simultaneously  present ;  it 
loses,  however,  its  trustworthiness  if  considerable  quantities  of 
cyanogen  are  present. —  Chemiker  Zeitung ;  Chem.  News,  Sptb.  16, 
1892,  p.  144. 
VOLUMETRIC   ESTIMATIONS   AND  ANALYTICAL 
SEPARATIONS  BY  MEANS  OF  POTASSIUM 
FERROCYANIDE  AND  FERRI- 
CYANIDE.1 
By  C.  Luckow. 
The  use  of  potassium  ferrocyanide  is  somewhat  restricted,  as  so 
many  ferrocyanides  are  insoluble.  For  instance,  in  the  important 
titration  of  zinc  ores  it  is  necessary  to  remove  iron  and  other  metals 
before  titrating  with  the  ferrocyanide.  The  author,  therefore,  has 
made  an  attempt  to  introduce  ferricyanide  instead.  Having  pre- 
pared a  potassium  ferricyanide  free  from  sulphates  and  chlorides,  it 
was  found  that  this  substance  may  be  used  in  acid  solutions  even  in 
1  Chem.  Zeit.,  15,  1491  ;  Jour.  Chem.  Soe.,  1892,  p.  1129. 
