ON  THE  SUBLIMATION  OP  THE  ALKALOIDS. 
433 
of  a  method  so  successful  in  detecting  and  identifying  minute 
quantities  of  arsenious  acid  and  corrosive  sublimate  ;  and  he  lays 
claim  to  originality,  inasmuch  as  he  does  not  find  the  sublima- 
tion of  the  alkaloids  described  in  any  handbook  of  chemistry  or 
forensic  medicine,  even  the  most  recent.  This  claim  to  original- 
ity is,  1  believe,  fully  justified,  though  probably  every  manu- 
facturing chemist  must  have  recognized  the  fact  that  some,  at 
least,  of  the  alkaloids  are  sublimed  by  heat,  and  experimenters 
on  the  small  scale  must  have  observed  that  the  alkaloids,  as  a 
class,  after  melting,  and  before  depositing  carbon,  give  out  a 
more  or  less  dense  vapor  or  smoke,  which,  if  allowed  to  settle  on 
a  cool  surface,  might  possibly  present,  under  the  microscope, 
characteristic  appearances. 
This  new  application  of  the  test  of  sublimation  suggested 
itself  to  Dr.  Helwig  after  becoming  acquainted  with  the  simple 
methods  of  obtaining  sublimates  of  arsenic  and  mercury  on  flat 
surfaces,  with  a  view  to  microscopic  and  chemical  examination, 
which  I  proposed  in  the  year  1858.*  His  own  method  of  pro- 
cedure with  the  alkaloids  is  as  follows  : — -In  a  piece  of  platinum 
foil  of  moderate  thickness,  a  small  cup-like  hollow  is  formed;  in 
this  a  minute  quantity  of  the  alkaloid  is  placed,  and  over  it  a 
microscopic  slide  (Objects -tiger).  This  simple  apparatus  being 
placed  on  a  suitable  support,  the  flame  of  a  spirit-lamp,  is  cau- 
tiously applied  until  the  alkaloid  melts,  from  which  point  of  time 
the  sublimate  begins  to  form  on  the  glass  slide. 
Now,  this  mode  of  procedure  is  obviously  open  to  objection. 
The  successive  changes  that  take  place  in  the  alkaloid — the  dis- 
coloration, the  liquefaction,  the  deposit  of  carbon,  either  on  the 
spot  (as  happens  with  some  alkaloids)  or  over  a  wide  surface 
traversed  by  the  liquid  (as  in  the  case  with  others) — cannot  be 
distinctly  seen,  and  some  diagnostic  marks  of  the  alkaloids  as  a 
class,  and  among  themselves,  are  thus  lost.  Nor,  again,  can  the 
formation  of  the  sublimate  itself  be  seen  and  watched,  as  it 
*On  the  Production  and  Identification  of  Crystals  of  Arsenious  Acid 
and  Crusts  of  Metallic  Arsenic,"  (Beale's  "Archives  of  Medicine,"  No. 
iii.,  1858;)  also  "On  the  Microscopic  Characters  of  the  Crystals  of  Arse- 
nious'Acid,"  ("  Journal  of  th  •  Microscopic  Society,  1861,"  and  "Prin- 
ciples of  Forensic  Medicine,"  2d  edit.,  1861,  p.  372.) 
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