MERCURY — ITS  OXIDES  AND  ACETATES,  ETC.  267 
portion  of  the  oxide.  The  oxide  as  prepared  both  by  the  U.  S. 
Pharmacopoeia  and  the  process  of  Duflos,  contains  metallic  mer- 
cury and  red  oxide  of  mercury. 
3d.  The  oxides  of  mercury  in  solution  in  water  are  complete- 
ly precipitated  in  a  metallic  state  by  tannic  acid — the  reaction 
occurring  in  the  cold  as  well  as  by  application  of  heat.  The 
oxides  are  insoluble  in  pure  washed  ether,  and  in  strong  alcohol. 
Heated  solutions  of  cane  or  grape  sugar  do  not  precipitate  them 
from  aqueous  solutions.  Hydrocyanic  acid  with  black  oxide  of 
mercury  throws  down  half  the  mercury  and  forms  cynanide  of 
mercury. 
4th.  Acetate  of  mercurous  oxide  is  resolved  by  boiling  water 
into  mercury,  and  acid  solutions  of  mercuric  and  mercurous  ace- 
tate. 
5th.  Acid  solutions  of  mercuric  acetate  are  under  no  circum- 
stances affected  by  ammonia. 
6th.  If  the  acetic  acid  contains  alcohol,  heat  converts  a  por- 
tion of  the  mercuric  acetate  into  mercurous  acetate,  with  produc- 
tion of  acetic  ether. 
7th.  Chlorides  do  not  precipitate  solutions  of  mercurous  ace- 
tate so  completely  that  sulphide  of  ammonium  does  not  affect  the 
filtrate.  Caustic  potash,  however,  does  not  affect  the  solution 
after  close  filtration. 
We  have  then  as  causes  from  which  errors  may  arise  in  exam- 
ining for  oxide  of  mercury  in  blue  mass, 
1st.  The  solubility  of  both  oxides  in  hot  water  to  a  notable 
extent,  and  the  conversion  of  the  oxide  into  metallic  mercury  by 
the  tannic  acid  contained  in  the  rose  leaves. 
2d.  The  solubility  of  calomel  in  highly  dilute  solutions,  in 
dilute  hydrochloric  acid,  as  also  in  large  excess  of  the  solutions 
of  the  chlorides,  thus  affording  no  results  with  these  reagents. 
3d.  The  partial  conversion  of  mercuric  into  mercurous  acetate 
when  heated  with  excess  of  acetic  acid,  which  contains  alcohol 
as  an  impurity. 
4th.  The  conversion  by  boiling  of  acetate  of  mercurous  oxide 
into  mercury,  and  the  salts  of  both  oxides. 
5th.  Ammonia  affording  no  reaction  with  the  acetate  of  mer- 
curic oxide  when  the  solution  is  acid. 
6th.  The  difficulty  of  precipitating  salts  of  the  black  oxide  by 
