MERCURY — ITS  OXIDES  AND  ACETATES,  ETC.  265 
evident  reaction  with  sulphide  of  ammonium  ;  at  215°  F.  a  much 
larger  portion  of  the  oxide  is  taken  up,  giving  a  deep  brown 
color  on  addition  of  sulphide  of  ammonium. 
Water,  which  had  been  heated  over  the  red  oxide,  and  after 
decanting  allowed  to  stand  twenty-four  hours,  gave  a  much 
stronger  reaction  with  alkaline  sulphides,  than  was  obtained 
from  the  cold  solution.  But  the  reaction  is  more  feeble  than 
with  the  black  oxide. 
Tannic  acid  precipitates  the  mercury  from  the  aqueous  solution 
of  the  red  oxide  as  metallic  mercury.  This  reaction  takes 
place  in  the  cold,  but  more  quickly  when  heated. 
Red  oxide  of  mercury  is  completely  insoluble  in  cold  alcohol  of 
95  per  cent.,  also  insoluble  in  concentrated  sulphuric  ether 
(free  from  acid)  when  saturated  with  water. 
Mercuric  oxide  gradually  blackens  when  exposed  to  sunshine, 
"  being  resolved  (according  to  Guibourt,)  into  oxygen  and  me- 
tallic mercury,"  or  according  to  Donovan,  "  into  oxygen  and 
mercurous  oxide." 
"  Heated  solutions  of  sugar  reduce  it  (according  to  Vogel)  to 
mercurous  oxide.' ' 
Under  a  microscope,  mercuric  oxide  shows  translucent  orange- 
colored  crystals. 
Acetate  of  Mercurous  Oxide  "is  soluble  in  one  hundred  and 
thirty-three  parts  of  water,  at  53  or  59°  F.,  but  is  not  soluble 
in  cold  alcohol.  When  boiled  with  water,  it  is  resolved  into  11 
per  cent,  of  mercury,  and  a  solution  of  mercuric  and  mercurous 
acetate  containing  excess  of  acid." — Q-arot. 
"  Sugar  converts  it  into  mercury  and  black  oxide." — Vogel. 
Both  acid  and  neutral  solutions  of  mercurous  acetate  are  de- 
composed by  ammonia,  hydrochloric  acid,  and  the  soluble  metal- 
lic chlorides  "  visible  even  to  the  80,000ths  degree  of  dilution." 
(Pfaff,)  The  precipitates  by  hydrochloric  acid,  and  the  chlorides 
in  highly  dilute  solutions,  are  completely  soluble  in  excess  of  the 
precipitants  when  heated,  the  solutions  remaining  nearly  clear 
when  cold.  The  solubility  of  the  precipitates  is  more  apparent 
from  the  acid  than  from  the  neutral  solution. 
The  chlorides  do  not  precipitate  an  acid  or  neutral  solution, 
so  that  the  filtrate  is  not  affected  by  sulphide  of  ammonium  ;  it 
is  not,  however,  affected  by  potash. 
