ON  THE  SOLIDIFICATION  OF  CARBONIC  ACID. 
529 
Nearly  all  left  a  green  coloration  on  the  spot  after  the  lapse 
of  twenty-four  or  forty-eight  hours,  owing  to  the  reduction  of 
chromic  acid  to  sesquioxide  of  chrome. 
These  and  other  observations  I  have  made  in  regard  to  vege- 
table proximate  principles,  convince  me  of  their  general  and 
powerful  deoxidising  properties,  as  well  as  the  establishment  of 
the  fact  that  the  '''■color  test,'"  or  oxidising  test,'"  is  not  only 
delicate  but  characteristic,  and  consequently  reliable.  In  refer- 
ence to  the  delicacy  of  the  color  test"  I  found  that  when  one 
grain  of  pure  strychnine  was  dissolved  in  400,000  drops  of  dis- 
tilled water,  and  one  drop  of  that  solution  was  allowed  to  evapo- 
rate to  dryness  on  a  glass  plate,  not  only  were  the  crystals  of 
strychnine  revealed  by  the  microscope,  but  on  the  addition  of  a 
small  drop  of  very  white  concentrated  sulphuric  acid,  and  the 
subsequent  application  of  the  point  of  a  spicula  of  bichromate  of 
potassa,  the  characteristic  colors  were  brought  out. — Chemical 
News,  London,  Oct.  6,  1860. 
ON  THE  SOLIDIFICATION  OF  CARBONIC  ACID. 
By  mm.  a.  Loir  and  Ch.  Drion. 
In  a  paper  read  before  the  Academy,  June  2,  1860,  we  stated 
that  atmospheric  pressure  liquefies  carbonic  acid  when  its  tem- 
perature is  reduced  to  the  point  at  which  liquid  ammonia  evapo- 
rates in  vacuo.  By  slightly  modifying  the  conditions  of  the 
experiment,  we  have  succeeded  in  solidifying  carbonic  acid  with 
the  aid  of  an  apparatus  as  simple  as  those  daily  employed  in 
chemical  laboratories.  This  hitherto  dangerous  and  costly 
operation  may  in  future  be  easily  repeated  to  a  chemical  class. 
If  liquid  ammonia  is  introduced  into  a  glass  globe,  and  the 
interior  of  this  put  in  communication  with  a  good  air-pump,  by 
the  intervention  of  a  vessel  containing  coke  impregnated  with 
sulphuric  acid,  the  temperature  of  the  liquid  is  rapidly  reduced 
from  the  first  strokes  of  the  piston.  The  liquid  begins  to  so- 
lidify towards  81*^ ;  it  soon  becomes  a  mass,  and  if  the  air-pump 
allows  the  reducing  of  the  pressure  to  about  a  millimetre  of 
mercury,  the  temperature  of  the  solid  ammonia  becomes  lowered 
some  degrees  more  and  reaches  89-5''.    This  suffices  to  deter- 
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