Am'ribUri884arm'}        Ammonium  Chloride  and  Lead  Iodide.  93 
try  four  compounds  are  noticed  which  may  be  formed  and*  the  following 
information  is  given  as  to  their  formation,  composition  and  properties  : 
Lead  iodide  is  completely  soluble  in  both  hot  and  cold  solutions  of 
ammonium  chloride.  The  hot  solution  on  cooling  deposits  crystals 
having  the  formula  NH4Cl.PbI2  (Volckel)  and  (NH4Cl)3.(PbI2) 
("  Behrens,  Pogg.  Ann."  lxii,  252).  The  first  are  described  as  yellowish 
white  needles,  the  second  as  yellowish  needles,  having  a  beautiful  silky 
lustre.  The  yellow  acicular  crystals,  which  are  deposited  from  the 
hot  solution,  according  to  Poggiale,  do  not  contain  any  ammonium 
chloride  and  have  the  formula  (PbCl2)2.PbI2.  After  concentration  the 
mother  liquor  deposits  white  branching  needles  of  a  silky  lustre,  which 
contain  ammonium  chloride,  become  yellow  on  exposure  to  air,  and  are 
decomposed  by  water;  their  formula  is  (NH4Cl)4.PbI22H20  (" Pog- 
giale, Compt.  Kend."  xx,  1180.) 
On  applying  the  test  as  proposed  by  Hager  and  admitted  by  the 
Pharmacopoeia,  the  change  of  the  mixture  in  color  from  yellow  to 
white  is  most  likely  due  to  the  formation  of  lead  chloride  and  ammo- 
nium iodide,  both  of  which  salts  are  white ;  possibly  a  double  chloride 
may  be  formed,  or  a  white  double  salt  containing  both  iodide  and 
chloride.  On  the  application  of  heat  the  lead  iodide  is  reproduced 
before  it  is  dissolved  with  the  formation  of  one  or  more  of  the  above- 
mentioned  double  salts.  A  reproduction  of  lead  iodide,  either  wholly 
or  in  part,  also  takes  place  on  diluting  the  mixture  with  cold  water. 
The  solubility  of  lead  iodide  in  ammonium  chloride  was  already 
observed  in  1827  by  Boullay  ("Ann.  Chim.  Phys.,"  xxxiv).  But 
Wittstein  appears  to  have  first  studied  the  effect  of  ammonia  and  its 
salts  upon  lead  iodide  ("Buchner's  Report.,"  1838,  liii,  322);  he  founcl 
that  solutions  of  ammonium  carbonate  and  sulphate  change  the  yellow 
color  of  lead  iodide  rapidly  to  white,  and  that  the  same  change  though 
less  rapidly,  also  takes  place  with  ammonia  and  with  ammonium  nitrate 
and  succinate.  Very  likely  all  freely  soluble  ammonium  salts  have 
the  same  effect. 
The  influence  of  ammonium  salts  upon  lead  chromate  does  not  appear 
to  have  been  the  subject  of  investigation;  at  least  I  have  found  nothing 
in  works  of  reference  beyond  the  statement  that  chrome  yellow  is 
insoluble  in  ammonium  chloride.  This,  as  shown  above,  is  correct; 
yet  a  notable  change  takes  place  on  boiling  with  a  solution  of  the  latter 
salt,  indicating  the  production  of  basic  lead  chromate  or  chrome  red. 
Before  summing  up  I  would  like  to  call  attention  to  a  misplacement 
