^^'I^TiiJm^'^'}    Crystallized  Mermrous  Iodide  and  Bromide,  197 
cant  it  has  superior  qualities  to  all  animal  or  vegetable  oils,  owing  to 
its  freedom  from  oxygen,  as  well  as  its  cheapness  in  comparison  with 
these  oils.  Its  use  as  the  cheapest  of  fuels  is  of  the  first  importance, 
although,  we  may  say,  as  yet  in  its  infancy  for  this  purpose ;  but  that 
it  will  ultimately  displace  coal  in  the  merchant  and  naval  marine 
of  all  nations,  is,  in  my  opinion,  but  a  question  of  no  very  distant 
time. 
Whether  from  a  scientific  or  commercial  point  of  view  we  must  all 
admit  that  it  would  be  a  great  loss  to  mankind  if  the  supplies  of  this 
almost  invaluable  natural  product  were  at  no  distant  date  to  be  ex- 
hausted, and  for  this  reason  I  considered  it  might  be  of  special  interest 
to  bring  the  question  of  its  origin  under  your  notice,  and  I  trust  I 
have,  however  crudely,  succeeded  in  placing  before  you  the  various 
opinions  of  those  best  qualified  to  form  a  judgment  on  the  question  at 
issue. 
CEYSTALLIZED  MERCUROUS  IODIDE  AND  BROMIDE. 
By  a.  Stroman. 
If  a  saturated  solution  of  mercurous  nitrate,  as  free  as  possible  from 
oxide  and  slightly  acidified  with  nitric  acid,  is  heated  to  boiling  with 
iodine,  the  latter  becomes  covered  with  a  yellow  powder,  which  partial- 
ly dissolves,  and  the  solution,  after  decantation  into  a  warm  dish, 
deposits,  in  the  dark,  lustrous,  yellow,  transparent,  tetragonal  scales  of 
mercurous  iodide ;  these  must  be  dried  in  the  dark  at  the  ordinary  tem- 
perature. When  the  mercurous  nitrate  solution  is  treated  with  an  alco- 
holic solution  of  iodine  in  the  cold,  small,  yellow  spangles  of  mercu- 
rous iodide  are  obtained;  but  the  product  formed  by  the  old  methods  of 
preparation,  that  is,  by  rubbing  together  molecular  proportions  of  mer- 
cury and  iodine,  and  by  adding  potassium  iodide  in  solution  to  a  solu- 
tion of  mercurous  salt,  have  a  green  color,  and  are  impure,  although 
the  pure  yellow  compound  can  be  obtained  by  reversing  the  last  process 
and  adding  an  excess  of  a  dilute  solution  of  mercurous  nitrate  to  potas- 
sium iodide  in  solution.  The  crystallized  compound  shows  the  same 
color-changes  as  observed  by  Yvon  (this  Journal,  1873,  p.  474  and  525), 
but  the  change  does  not  begin  at  60°,  as  stated  by  him,  since  the  salt 
is  still  a  pure  yellow  at  100°,  and  only  passes  from  this  color  through 
dark  yellow  and  orange  to  garnet-red  at  higher  temperatures.  Sublima- 
