Prep.  1.  Arsenious  acid,  in  fine  powder,  2
parts ;  concentrated  nitric  acid,  6  parts;  hydro-
chloric acid,  1  part ;  mix  in  a  flask  or  tubu-
lated retort,  and  digest,  with  beat,  until  solu-
tion is  complete ;  after  repose,  decant  the  clear
portion  and  evaporate,  to  the  consistence  of  a
thick  .syrup.
2.  Dissolve  arsenious  acid  in  hot  hydro-
chloric acid,  and  when  the  solution  is  cold  add
concentrated  nitric  acid,  in  small  quantities  at
a  time,  until  red  vapours  cease  to  be  evolved,
then  proceed  as  before.
Prop.  Thick  syrup,  occasionally  forming
clear  transparent  crystals,  very  deliquescent,
readily  soluble  in  water,  and  converted  by
heat  into  the  anhydrous  acid.  Extremely
poisonous.
Arseniates.  Prep.  Most  of  the  metallic
arseniates  may  be  formed  by  adding  a  solution
of  a  soluble  salt  of  the  metal  to  another  of  an
alkaline  arseniate,  as  long  as  a  precipitate
falls;  which  must  be  collected,  washed,  and
dried.  The  alkaline  arseniates  may  be  pre-
pared by  adding  the  base  or  its  carbonate  to
a  solution  of  the  acid,  to  alkaline  reaction,
and  then  evaporating  and  crystiillising  the
liquid.
Prop.,  ^0.  The  arseniates  of  the  alkalies  are
soluble  in  water;  those  of  the  earths  and
metals  insoluble,  except  in  acids.  They  are
isomorphous  with  the  corresponding  phos-
phates.
2'esta.  Nitrate  of  silver  added  to  the  solu-
tion ot  an  arseniiite  gives  a  highly  character-
istic reddish-brown  precipitate,  which  distin-
guishes It  from  arsenious  acid.  Nitrate  of
lead  gives  a  white  precipitate,  and  the  salts
of  copper  greenish- blue  ones.  Pure  lump,
sugar  dissolved  in  an  aqueous  solution  of  this
acid  becomes,  in  u  few  hours,  of  »  reddish
colour,  and  afterwards  of  a  magnificent  purple.
Heated  with  charcoal  it  evolves  a  garlic-like
odour,  and  is  reduced  to  the  metallic  state.
