532 
CARBONATE  OF  POTASH. 
Both  these  inconveniences  may  be  remedied  by  the  substitu- 
tion of  bicarbonate  of  soda  for  the  carbonate.  When  this  salt 
is  heated  to  redness,  it,  as  is  well  known,  loses  one  of  its  two 
equivalents  of  carbonic  acid  and  all  its  water,  a  pure  mono-car- 
bonate remaining.  Bicarbonate  of  soda  of  commerce  is  nearly 
always  almost  pure,  never,  as  far  as  my  experience  goes,  con- 
taining more  than  slight  traces  of  chlorides  and  sulphates. 
When  not  heated  beyond  redness,  the  resulting  carbonate  is  not 
hard,  but,  on  the  contrary,  is  a  loosely  cohering  perfectly  white 
powder.  The  slight  difference  in  the  cost  of  carbonate  and  bi- 
carbonate is  of  small  moment  when  compared  with  the  saving  of 
time  and  trouble,  and  the  superiority  of  the  dried  carbonate 
made  from  the  latter  salt — Lond.  Ohem.  I^ews,  July  13,  1861, 
from  Dublin  Medical  Press. 
CARBONATE  OF  POTASH. 
The  amount  of  water  which  carbonate  of  potash  contains  has 
been  debated  by  several  chemists.  Wackenroder,  Phillips, 
Berard  and  Giese,  and  now  Dr.  J.  J.  Pohl  (^Sitzungsber  d.  AJcad, 
der  Wissensch.  zu  Wien.,  bd.  xli.  s.  630)  have  severally  ex- 
amined the  salt  with  a  view  to  its  determination.  The  last 
found  in  a  saturated  solution  of  potash  which  had  been  kept  in 
a  stoppered  bottle  for  more  than  a  year,  some  six-sided  crystals 
which,  removed  into  the  air,  quickly  attracted  moisture  and 
liquefied.  The  qualitative  analysis  of  these  crystals  showed 
them  to  be  composed  of  potash,  carbonic  acid,  and  water,  with 
mere  traces  of  chlorine  and  sulphuric  acid.  When  heated  to 
100^  C.  they  lost  5-180  per  cent,  of  water.  Further  investiga- 
tions showed  that  they  contained  considerably  more  water, 
which  could  only  be  expelled  by  a  much  higher  temperature. 
The  salt  dried  over  sulphuric  acid  lost,  when  heated  to  redness, 
15-994  of  water,  and  had  the  following  composition  : — 
Carbonate  of  potash       ....  83-517 
Water  15-994 
Chlorine,  sulphuric  acid,  and  loss    •       .  0-489 
100.000 
This  closely  approaches  the  formula  2  (KOjCOg)  3H0,  which 
