262 
MERCURY — ITS  OXIDES  AND  ACETATES,  ETC. 
Black  oxide  of  mercury  is  insoluble  in  cold  alcohol  of  95  per 
cent,,  also  in  concentrated  sulphuric  ether,  (when  free  from 
acidity.)  Ether  saturated  with  water  does  not  dissolve  a  trace  ; 
cold  water  saturated  with  ether  dissolves  an  amount  which  may 
be  readily  detected. 
4th.  To  distilled  water,  which  had  been  boiled  over  the  oxide, 
and  filtered  while  warm,  five  grains  of  conf.  of  rose  were  added 
and  boiled  ;  after  close  filtration,  the  liquid  ceased  to  be  dis- 
turbed by  sulphide  of  ammonium. 
The  precipitated  matter,  when  warmed  with  dilute  nitric  acid, 
gave  a  brown  color,  with  sulphide  of  ammonium. 
5th.  Hot  distilled  water  holding  the  oxide  in  solution,  was 
not  deprived  of  it  by  boiling  with  cane  or  grape  sugar. 
6th.  To  a  warm  solution  of  the  oxide  in  distilled  water,  tannic 
acid  was  added,  and  the  solution  immediately  assumed  a  red  color, 
changing  to  pale  yellow  when  boiled.  After  standing  some 
hours,  a  slight  deposit  took  place ;  examined  under  a  glass  of 
considerable  power,  it  had  the  appearance  of  a  minutely  divided 
powder  of  a  grey  color,  without  lustre.  The  precipitate  was 
collected  on  a  small  watch-glass,  washed  with  alcohol  to  remove 
any  organic  matter,  and  dried  ;  when  rubbed  with  the  point  of  a 
knife,  metallic  globules,  visible  to  the  unassisted  eye,  were  col- 
lected. The  liquid,  from  which  the  deposit  was  obtained,  ceased 
to  be  disturbed  by  sulphide  of  ammonium. 
7th.  One  part  of  the  oxide  was  added  to  three  thousand  parts 
of  distilled  water,  and  boiled  in  a  flask  ;  when  nearly  cool,  half 
of  one  part  of  tannic  acid  was  added ;  a  glass  tube  was  tightly 
adapted  to  the  mouth  of  the  flask,  with  the  remote  end  dipping 
to  near  the  bottom  of  a  test  tube,  containing  a  clear  solution  of 
caustic  baryta.  The  mouth  of  the  test  tube  was  closed  by  a 
stopper  of  cotton,  to  prevent  free  access  of  air ;  when  the  con- 
tents of  the  flask  where  heated,  the  color  passed  from  red  to  pale 
yellow  ;  the  bubbles  passing  through  the  baryta  solution  caused 
it  to  become  turbid  ;  addition  of  nitric  acid  caused  effervescence, 
and  the  solution  became  clear. 
To  prove  this  experiment,  it  was  repeated,  omitting  the  tan- 
nic acid;  the  baryta  water  did  not  show  any  indications  of  car- 
bonic acid,  from  the  contents  of  the  flask. 
The  solution  containing  the  oxide  after  treatment  with  tannin, 
