Am.  Jonr.  Phaim. 
April,  HS8. 
Formaldehyde. 
197 
This  converter  consists  of  two  concentric  copper  tubes,  the  space 
between  which  is  filled  with  broken  coke  or  other  material  of  a 
similar  nature.  The  inner  tube  is  finely  perforated  with  many 
small  holes.  The  alcohol  vapor  is  admitted  into  this  inner  tube, 
and,  escaping  through  the  perforations,  is  oxidized  by  coming  in 
contact  with  the  heated  coke  and  the  copper  surface  of  the  outer 
tube. 
The  gases  produced  in  the  converter  pass  over  into  the  condenser. 
This  condenser  consists  of  a  cylindrical  tank  or  receiver,  which  may 
be  of  copper  ;  it  contains  a  coil  of  copper  pipe,  through  which  circu- 
lates a  refrigerating  mixture  capable  of  reducing  the  temperature  in 
the  tank  to  about  0°  C,  at  which  temperature  formic  aldehyde 
condenses  into  a  clear,  very  mobile  liquid,  which  boils  at  2i°C, 
and  which  polymerises  at  200  C. 
After  undergoing  certain  processes  of  purification,  enough  water 
is  added  to  form  a  40  per  cent,  solution. 
This  solution  is  not,  strictly  speaking,  a  solution  of  formaldehyde, 
but  of  para-formaldehyde,  as  the  pure  formaldehyde  polymerises 
the  moment  the  temperature  rises  above  200.  It  is  this  property 
which  renders  the  addition  of  water  or  alcohol  necessary. 
Formaldehyde  ^^//^.---Paraformaldehyde,  dried  in  the  pres- 
ence of  sulphuric  acid,  becomes  less  soluble  in  water.  The  insolu- 
ble part  constitutes  trioxymethylene,  a  white  powder  resolving  by 
heat  into  pure  formic  aldehyde.  This  powder  is  pressed  into  pas- 
tilles and  in  that  form  used  as  an  antiseptic  and  deodorant. 
Analysis  of  Formaldehyde. — f  1)  To  detect  its  presence.  Trillat's 
method.  An  aqueous  solution  of  aniline  is  obtained  by  dissolving 
3  grammes  of  fuchsin  or  magenta  in  I  litre  of  distilled  water ;  mix 
in  a  test  tube  20  c.c.  of  this  solution  with  20  ex.  of  the  liquid  to  be 
assayed.  In  the  presence  of  formic  aldehyde  a  very  light  cloud 
forms  after  several  hours.  This  reaction  is  very  delicate  ;  by  it  for- 
maldehyde can  be  detected  in  a  solution  of  2"o"o"o"o*  ^n  solutions  of 
this  attenuation,  however,  the  reaction  does  not  appear  until  after 
the  lapse  of  several  days. 
The  search  for  formaldehyde  in  alimentary  substances  is  often 
futile,  because  it  forms,  with  certain  organic  substances,  combina- 
tions from  which  it  cannot  be  separated. 
Quantitative  Analysis. — To  a  solution  of  3  grammes  of  aniline  in 
I  litre  of  water  is  added,  drop  by  drop,  thoroughly  shaking,  from 
