PREPARATION  OF  SOD^  CARBONAS  SICCATA.  531 
ered  with  an  unctuous  matter.  If  one  of  these  crystals  is  kept 
between  the  thumb  and  forefinger,  it  soon  produces  an  intole- 
rable burning. 
An  experiment  was  performed  by  placing  a  certain  quantity 
of  solid  carbonic  acid  in  a  small  glass  tube  communicating  with 
a  receiver  filled  with  mercury.  After  some  time  the  crystals 
disappeared,  leaving  no  residue,  while  the  receiver  was  filled 
with  perfectly  pure  carbonic  gas,  capable  of  being  completely 
absorbed  by  potash.  Mixed  with  ether  in  a  small  porcelain 
crucible,  these  carbonic  acid  crystals  yield  a  freezing  mixture 
of  a  temperature  of  81^. 
As  a  conclusion  to  these  summary  indications,  we  will  add 
that  the  liquid  ammonia  used  in  our  experiments  was  prepared 
by  M.  Bussy's  process — that  is  to  say,  by  acting  on  ammoniacal 
gas  in  a  globe  surrounded  with  liquid  sulphurous  acid,  the 
evaporation  of  which  is  expedited  by  an  air-pump.  By  this 
method  nearly  two  decilitres  of  liquid  ammonia  can  be  easily 
obtained  in  less  than  two  hours. 
We  determined  the  temperatures  here  indicated  by  means  of 
an  alcoholic  thermometer,  on  which  we  marked  two  fixed  points 
— that  is  to  say  0°  at  melting  ice,  and  40^^  at  the  temperature 
of  melting  mercury. — Lond,  Chem.  News,  July  13,  1861,  from 
Ocmptes  Rendus. 
ON  AN  IMPROVED  METHOD  OF  PREPARING  SOD^  CARBONAS 
SICCATA. 
By  Harry  Napier  Draper,  F.  C.  S.  L. 
The  directions  of  the  three  British  Pharmacopoeias  for  the 
preparation  of  dried  carbonate  of  soda  are  in  almost  every  re- 
spect alike.  Crystals  of  carbonate  of  soda  are  exposed  to  the 
action  of  heat  until  the  whole  of  their  water  is  dispelled.  This 
process  has  two  disadvantages :  1.  The  carbonate  of  soda  of 
commerce,  which  is  always  used  in  practice  to  the  exclusion  of 
the  pure  product  of  the  Pharmacopoeias,  invariably  contains 
sulphates  and  chlorides.  These,  are,  of  course,  found  also  in 
the  dry  salt.  2.  The  hard  cake  which  results  from  the  desic- 
cation of  the  crystals  is  extremely  difiicult  to  powder,  and  never 
makes  a  really  elegant  preparation. 
