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SUBLIMING  TEMPERATURES  OF  POISONS. 
1.  Sublimation  without  change  of  Form  or  Color. — This  class 
comprises  corrosive  sublimate  and  calomel,  arsenious  acid  and 
cantharidin,  which,  if  the  heat  is  gradually  increased,  and  then, 
maintained  at  or  near  the  temperature  indicated,  are  gradually 
dissipated  in  white  vapor,  and  leave,  if  pure,  no  residue. 
This  graduated  sublimation,  therefore,  differs  somewhat  from 
the  quicker  process  with  the  spirit-lamp  and  platinum-foil,  which 
places  the  four  substances  in  two  classes ;  the  one  containing 
arsenious  acid  and  calomel,  which  do  not  melt,  but  are  converted 
into  white  fumes,  without  residue  ;  the  other  corrosive-sublimate 
find  cantharidin,  which,  as  the  heat  is  usually  applied,  first 
melt,  and  then  disperse  in  white  vapor,  leaving  also  no  residue. 
The  subliming  temperatures  of  the  four  poisons  are  as 
follows : — 
Corrosive  sublimate,  at  or  about    .        .    200°  Fahr. 
Cantharidine  "  .        .  212° 
Calomel  "  .        .    240°  " 
Arsenious  acid  "  .       .    280°  " 
As  this  temperature  of  280°,  for  arsenious  acid,  is  very  low 
compared  to  that  commonly  assigned  (370°  to  400°),.  I  have 
carefully  repeated  the  experiments  with  this  poison,  and  find  a 
distinct  sublimate,  showing  crystals  under  the  microscope  at  this 
temperature.  To  obtain  large  sparkling  crystals  a  higher  tem- 
perature is  required.  I  have  also  obtained  sublimates  in  several 
reduction-tubes  immersed  in  a  sand  bath  side  by  side  with  the 
thermometer  at  a  temperature  never  exceeding  300°  ;  and  some 
of  these  consisted  of  large  sparkling  crystals.  On  referring  to 
works  of  authority,  I  find  the  subliming  temperature  of  arseni- 
ous acid  variously  stated — by  Miller  and  Bloxam  at  380°,  and 
in  the  British  Pharmacopoeia  at  400°  (not  exceeding  400°).  Dr. 
Taylor  places  it  at  the  low  figure  of  370°.  All  these  figures 
much  exceed  the  temperature  indicated  in  my  own  experiments ; 
and,  as  the  small  quantities  which  I  employed  cannot  account 
for  the  discrepancy,  I  am  at  a  loss  to  explain  it.  I  ought,  per- 
haps, to  state  that,  in  the  experiments  with  the  small  reduction- 
tubes,  I  used  fragments  of  solid  arsenious  acid,  none  of  which 
could  have  exceeded  a  grain  in  weight. 
If  this  first  group  were  enlarged  so  as  to  embrace  substances 
