248 
ON  GOLD  IN  THE  FORM  OP  MALLEABLE  SPONGE. 
the  tints  in  reflected  light  and  the  complementary  body-color, 
viz.,  whilst  sulphate  of  iodo-quinine  gives  a  cantharidine-green 
reflected  tint,  and  a  pink,  ruby-red,  reddish-brown  or  black  body- 
color  when  polarized  perpendicular  to  the  axis,  according  to  the 
thickness  of  the  plate  examined,  the  sulphate  of  iodo-cinchonidine 
is  golden-green  by  reflected  light,  and  gives  a  sky  or  indigo-blue 
or  black  "  body-color"  when  polarized  perpendicular  to  the  axis. 
I  have  not  yet  made  sufficient  chemical  analyses  of  this  substance 
to  enable  me  to  decide  on  its  formula,  but  I  have  obtained 
39-307  per  cent,  iodine  and  8-864  percent,  sulphuric  acid,  which 
sufficiently  indicate  a  chemical  difference  in  constitution  from 
the  sulphate  of  iodo-quinine,  which  it  may  be  remembered,  con- 
tains 32-609  per  cent,  iodine  and  10-61  per  cent,  sulphuric  acid. 
I  hope  soon  to  present  these  results  in  more  detail  when  suffi- 
cient leisure  is  afforded  me  for  the  purpose.— Qhemical  Gazette, 
March  2,  1857. 
ON  GOLD  IN  THE  FORM  OF  MALLEABLE  SPONGE. 
By  D.  Forbes,  F.  G.  S.* 
Of  late  years,  gold  in  a  peculiar  state  of  aggregation  has  been 
imported  from  America  for  the  use  of  the  dentists,  and  sold  at 
prices  between  £7  and  £8  per  ounce.  The  gold  is  in  the 
form  of  flat  cakes  about  two-tenths  of  an  inch  thick,  and  has  a 
reddish-brown  color  and  peculiar  spongy  texture. 
By  the  force  of  the  fingers  it  can  be  welded  or  kneaded  into 
a  pellet  without  crumbling,  and  becomes  by  the  pressure  of  a  tool 
nearly  as  solid  as  ordinary  gold.  It  is  therefore  well  adapted  for 
dental  purposes. 
The  process  by  which  it  is  said  to  be  made  is  patented  in 
America,  and  consists  in  repeatedly  dissolving,  precipitating, 
amalgamating,  heating,  &c,  so  extraordinary  that  it  is  probably 
only  put  forward  to  deter  others  making  it.  On  trial,  gold  of 
a  similar  spongy  character  was  obtained  by  the  following 
method  : — 
Gold  free  from  copper  is  dissolved  in  nitrohydrochloric  acid, 
keeping  an  excess  of  gold  in  the  solution  towards  the  close  of 
the  operation,  so^as  to  get  rid  of  all  nitric  acid  and  avoid  sub- 
sequent evaporation ;  any  chloride  of  silver  present  is  filtered 
