ON  PYRODEXTRINB. 
These  results  were  checked  by  a  second  analysis,  and  the  fol- 
lowing numbers  were  obtained  : — 
82.30  per  cent,  of  arsenious  acid. 
17.31  per  cent,  of  soda. 
99.61. 
Seeing  that  a  perfect  decomposition  of  the  carbonate  of  potash 
and  carbonate  of  soda  might  be  effected  by  using  an  excess  of 
arsenious  acid,  I  then  tried  the  exact  proportions  ordered  in  the 
London  Pharmacopoeia  for  making  the  liquor  potassse  arsenitis, 
viz.,  equal  parts  of  arsenious  acid  and  carbonate  of  potash.  I 
weighed  very  accurately  five  grammes  of  each,  and  boiled  them 
with  ten  ounces  of  distilled  water  in  a  flask,  until  all  the  arseni- 
ous acid  was  dissolved.  After  boiling,  there  remained  six  ounces 
of  liquid.  I  then  determined  the  percentage  of  carbonic  acid 
in  it,  and  instead  of  finding  .8535  per  cent.,  which  I  should  have 
found  had  no  decomposition  taken  place,  I  only  obtained  .334 
per  cent.  By  calculation,  I  find  that  if  the  arsenious  acid  had 
decomposed  its  equivalent  of  carbonate  of  potash,  the  solution 
should  have  contained  .2575  per  cent,  of  carbonic  acid,  which  is 
only  about  ^  of  a  per  cent,  less  than  I  really  found. 
I  think  this  clearly  shows  that  a  decomposition  of  the  carbo- 
nate of  potash  does  take  place,  and  the  solution  contains  arsenite 
of  potash  and  undecomposed  carbonate  of  potash,  the  undecom- 
posed  carbonate  being  due  principally  to  the  fact,  that  more 
carbonate  of  potash  is  used  than  the  arsenious  acid  is  capable  of 
decomposing. — London  Pharm.  Journ.,  March,  1858. 
ON  PYRODEXTRINE. 
By  M.  Gelis. 
[The  following  is  extracted  from  a  report  to  the  French  Academy,  by 
Messrs.  Chevreul,  Regnault  and  Pelouze,  on  a  communication  of  M. 
Gelis  on  the  action  of  heat  on  organic  substances. — Ed.  Amer.  Jour. 
Phar.] 
This  brief  history  was  necessary  for  understanding  what  M. 
Gelis  has  added  to  the  question. 
He  did  not  study  the  colorless  compound,  desiring  to  know 
the  cause  of  the  coloration  of  roasted  starch,  bread-crust  &c.  ; 
