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ON"  PROTIODIDE  OF  MERCURY. 
11 
ON  PROTIODIDE  OF  MERCURY. 
By  John  M.  Maisch. 
The  last  Journal  of  Pharmacy,  on  page  517,  contained  some 
remarks  by  Mr.  Bullock  on  Boutigny's  process  for  the  prepara- 
tion of  iodide  of  mercury.  Wittstein's  Vierteljahresschrift,  V. 
536,  publishes  a  paper  on  a  similar  subject  by  Oscar  Lichten- 
berg,  who  tried  J.  B.  Sobry's  new  (?)  process,  published  in  the 
Journal  de  Pharm.  d'Anvers,  1855,  609,  which  consists  in  the 
double  decomposition  of  calomel  and  iodide  of  potassium  under 
the  aid  of  water.  Mr.  Lichtenberg  treated  finely  levigated 
calomel  with  a  solution  of  iodide  of  potassium,  and  obtained — 
what  was  to  be  expected — a  mixture  of  the  protiodide,  proto- 
chloride  and  metallic  mercury,  and  comes  to  the  conclusion  that 
by  Sobry's  process  the  desired  preparation  cannot  be  obtained. 
There  is,  however,  another  way  of  manipulating  in  order  to  in- 
sure the  double  decomposition,  viz  :  rubbing  the  dry  articles  well 
together  and  afterwards  treating  them  with  water.  These  are 
Boutigny's  directions,  who  employs  boiling  water  for  decomposi- 
tion and  washing. 
The  protiodide  of  mercury  is  a  very  easily  decomposable  body, 
not  only  by  the  light,  but  also  by  other  agents,  as  the  following 
few  quotations  will  show.  According  to  Otto,  it  has  little  con- 
stancy, and  from  different  causes  is  divided  into  mercury  and 
the  biniodide  or  sesqui-iodide  ;  such  causes  are  the  treatment  with 
hydriodic  acid,  iodide  of  potassium  and  similar  iodides.  Mitscher- 
lich  says  :  When  heated  gradually,  it  decomposes  into  mercury 
and  the  red  iodide  ;  the  same  result  is  obtained  on  treating  it 
with  a  solution  of  iodide  of  potassium  or  other  substances  that 
have  an  affinity  for  the  red  iodide.  This  decomposition,  accord- 
ing to  Mohr,  takes  place  by  the  action  of  many  chemical  pre- 
parations, especially  by  boiling  it  with  hydrochloric  acid,  the 
iodides,  sal  ammoniac  and  common  salt. 
If  the  protiodide  of  mercury  is  treated  with  a  solution  of 
iodide  of  potassium  at  ordinary  temperature,  it  quickly  assumes 
a  dark  green,  almost  black  color ;  a  solution  of  chloride  of 
potasssium  produces  ultimately  the  same  change,  but  far  less 
rapidly  ;  but  at  a  boiling  heat  the  decomposition  is  perceptible 
instantly.    The  ordering  of  hot  water,  therefore,  must  appear 
