276      ESTIMATION  OF  ALUMINA  BY  CARMINIC  ACID,  ETC. 
the  liquid  was  found  to  retain  all  its  properties  while  assuming 
the  spheroidal  state,  and  was  still  able  to  freeze  mercury  con- 
tained in  little  glass  ampullge.  Finally,  the  liquid  protoxide  be- 
came solidified  under  the  recipient  of  an  air-pump,  the  tempera- 
ture being  reduced  to  120°  below  zero,  Centigrade — the  most 
intense  cold  yet  obtained. — Med.  News,  Jan.,  1865. 
THE  ESTIMATION  OF  ALUMINA  BY  CARMINIC  ACID,  AND 
THE  ACTION  OF  SOxME  REAGENTS  ON  CARMINATES. 
By  M.  C.  Luckow. 
A  solution  of  cochineal  or  carminic  acid  has  the  property  of 
coloring  carmine,  a  liquid  containing  alumina ;  when  acidulated 
this  liquid  turns  orange.  The  author  has  taken  advantage  of 
this  reaction  to  make  some  analytical  researches  on  alumina. 
The  following  are  the  results  he  has  obtained.  Carbonate  of 
soda  precipitates  alumina  imperfectly ;  in  the  presence  of  an 
ammoniacal  salt  the  precipitation  is  more  complete ;  with  bicar- 
bonate of  soda  instead  of  soda  it  is  almost  perfect.  The  more 
slowly  the  cold  precipitation  by  carbonate  of  ammonia  is  effected, 
the  more  complete  it  is.  The  precipitate  obtained  with  bicar- 
bonate is  less  bulky  than  that  obtained  with  neutral  carbonates, 
and  is  consequently  more  easily  washed. 
The  precipitation  of  alumina  by  carbonate  of  ammonia  or 
ammonia  is  complete  if  the  liquid  is  boiled  until  it  returns  to 
its  neutral  state.  The  filtered  liquid  does  not  give,  with  car- 
minic acid,  the  reaction  characteristic  of  alumina. 
The  cold  precipitation  by  ammonia  or  by  sulphide  of  ammo- 
nium is  more  complete  the  longer  the  time  taken  to  effect  it, 
and  the  smaller  the  excess  of  ammonia  and  the  greater  the  ex- 
cess of  sulphide  the  better. 
By  passing  a  current  of  carbonic  acid  into  a  solution  of  alka- 
line alumina,  the  precipitation  of  this  base  is  almost  perfect. 
By  boiling  an  alkaline  solution  of  alumina  with  chloride  of 
ammonium  until  the  reaction  is  no  longer  alkaline,  the  alumina 
is  completely  precipitated. 
Alkaline  carminates  are  soluble  in  water,  very  little  so  in 
alcohol their  solution  is  of  a  red  violet  color.  Alkaline  earthy 
