ON  THE  PREPARATION  OF  IODIDE  OF    POTASSIUM.  319 
ing  varnish,  when  the  mass  immediately  appears  ready  to  boil 
over,  entirely  in  consequence  of  the  slight  moisture  introduced 
into  it  by  the  breath. 
When  the  varnish  is  prepared,  it  is  poured  through  a  fine  wire 
sieve,  and  then  allowed  to  settle  sufficiently.  Filtration  through 
pointed  bags,  as  recommended  by  Miller,  appears  to  the  author  to 
take  up  a  great  deal  too  much  time,  is  unquestionably  attended 
with  loss,  and  does  not  lead  to  the  desired  object  so  well  as 
standing  quietly. 
By  this  method,  two  workmen  in  the  author's  factory  prepare 
4-5  cwts.  of  good  varnish  per  day. 
If  it  be  desired  to  give  the  varnish  a  tougher  consistence,  2-3 
per  cent,  of  good  bleached  linseed-oil  (not  boiled  with  oxide  of 
lead)  must  be  added  to  it  before  boiling.  This  communicates 
great  toughness  to  it,  and  it  then  resists  friction,  &c.  much 
better. — Ibid,  from  Polytechnisches  Centralbl.,  1854,  p.  168. 
ON  THE  PREPARATION  OF  IODIDE  OF  POTASSIUM. 
By  A.  Overbeck. 
The  author  gives  the  following  prescription  for  the  preparation 
of  iodide  of  potassium  : — 
Iodide  of  formyle  is  prepared  from  3  equivs.  alcohol,  6  equivs. 
iodine,  and  5  equivs.  potash.  If  4  equivs.  of  iodine  be  employed 
to  C4  HG  O2,  the  mass  thickens  too  much  by  separation  of  the 
iodide  of  formyle  produced,  so  that  the  greater  addition  of 
alcohol  is  very  essential  to  the  facilitation  of  the  operation.  This 
is  performed  in  the  following  manner  : — 
The  necessary  quantity  of  watery  alcohol  (C4  H5  0,  HO)  is' 
first  gently  heated  in  a  beaker  or  flask ;  the  dry  iodine  and  the 
potash  (the  latter  dissolved  in  as  little  water  as  possible)  are  then 
alternately  added,  in  such  a  manner  that  before  each  addition  of 
iodine  the  solution  is  completely  decolorized.  The  iodide  of  for- 
myle produced  separates  for  the  most  part  during  the  operation 
in  citron-yellow  laminae ;  its  complete  separation  is  effected  by 
pouring  over  it  20  times  as  much  water  as  there  was  alcohol  em- 
ployed ;  the  whole  is  then  collected  on  a  filter,  pressed  between 
blotting-paper,  and  boiled  with  solution  of  potash  (1  equiv.  of 
