ON  OXIDE  OP  ZINC. 
435 
ON  OXIDE  OF  ZINC. 
By  Charles  Caspari. 
Hellot  was  the  first  who,  in  the  year  1735,  taught  the  prepa- 
ration of  the  Oxide  of  Zinc  by  the  pyro-chemical  process ;  and 
formerly  all  the  oxide  used  for  pharmaceutical  and  medical  pur- 
poses was  prepared  by  the  combustion  of  metallic  zinc.  It  was 
this  preparation  which,  in  former  years,  acquired  so  high  a 
reputation  as  a  therapeutical  agent,  under  the  names  of  Calx 
Zinci,  Flores  Zinci,  Lana  Philosophica,  Pompholix,  Oxidum 
Zinci,  Nihilum  Album,  etc.  To  prepare  it  in  this  manner,  we 
expose  metallic  zinc  to  a  red  heat  in  a  deep  crucible,  placed 
somewhat  obliquely  in  a  good  blast  furnace.  The  vapors,  aris- 
ing from  the  zinc,  will  absorb  oxygen  from  the  air,  take  fire, 
and  burn  with  a  splendid  greenish-blue  shining  flame.  The 
oxide,  thus  formed,  covers  partly  the  sides  of  the  crucible  and 
partly  the  molten  metal,  in  the  form  of  white  flocks,  which 
have  to  be  removed,  now  and  then,  with  an  iron  spoon,  so  as 
not  to  interrupt  the  oxidation  of  the  zinc,  and  to  allow  a  free 
access  of  air.  To  remove  all  particles  of  metal,  the  oxide, 
when  cold,  is  washed  frequently  with  water,  passed  through  a 
sieve,  and  then  dried.  The  metallic  zinc  ordinarily  occurring 
in  commerce  is  never  entirely  free  from  other  metals,  and  when 
oxidized  in  the  above  manner,  part  of  the  contaminating  metals 
are  also  oxidized  and  will  be  mixed  with  the  oxide  of  zinc. 
However,  by  using  the  better  qualities  of  the  metal,  these  im- 
purities are  only  trifling  and  seem  not  to  have  lessened  its  ap- 
plication for  therapeutical  purposes.  Most  of  the  oxide  of  zinc 
now  in  use  is  hydro-chemically  prepared  by  precipitating  a  pure 
salt  of  zinc  in  such  a  manner  as  to  decompose  it  either  with 
carbonate  of  ammonia,  or  with  carbonate  of  soda.  The  follow- 
ing mode  of  preparation  seems  to  answer  well  all  the  demands 
required  of  it,  both  as  to  cheapness  as  well  as  the  quality  of  the 
product  thereby  obtained. 
Dissolve  17  ozs.  of  carbonate  of  soda  in  6  pints  of  water ; 
after  filtration,  heat  the  solution  to  the  boiling  point,  and  add 
to  it,  by  degrees,  continually  stirring,  a  filtered  solution  of  16 
ozs.  pure  sulphate  of  zinc  in  3  pints  of  water.  The  precipitate 
thus  obtained  is  not  gelatinous,  but  more  loose  powder-like,  and 
