618  Properties  and  Uses  of  Formaldehyde.  /Am- Jour- Pharm- 
November,  1896. 
tion  containing  40  per  cent,  of  the  aldehyde.  Most  of  the  pub- 
lished experiments  have  been  made  with  this  solution,  which  is 
placed  on  the  market  under  various  trade  names. 
Hoffman  discovered  formaldehyde  in  1867.  Loew  subsequently 
demonstrated  its  germicidal  powers,  and  Berlioz  and  Trillat  sug- 
gested its  use  as  a  powerful  disinfectant  free  from  poisonous  proper- 
ties. It  has  the  formula  HCHO,  is  a  powerful  reducing  agent,  and 
when  oxidized  yields  formic  acid.  A  solid  polymeric  variety — para- 
formaldehyde— is  also  known.  There  are  several  chemical  processes 
by  which  the  aldehyde  may  be  prepared,  but  the  most  practicable  is 
that  dependent  on  the  limited  oxidation  of  methylic  alcohol.  If  a 
current  of  air  charged  with  methylic  alcohol  vapor  be  passed  over 
a  coil  of  glowing  platinum  or  platinized  asbestos,  and  the  escaping 
gases  condensed  in  a  Liebig's  condenser,  a  weak  solution  of  formic 
aldehyde  in  methyl  alcohol  results.  The  substitution  for  the  plati- 
num spiral  of  a  roll  of  superficially  oxidized  copper  gauze  gently 
heated  in  a  glass  tube  through  which  the  mixed  vapors  are  passed, 
the  product  being  led  into  water,  greatly  increases  the  yield,  it 
being  possible  by  this  means  to  obtain  a  solution  containing  I  5  to 
20  per  cent,  of  formic  aldehyde.  The  commercial  solution,  "  forma- 
lin," is  understood  to  be  manufactured  by  a  similar  process  to  the 
foregoing,  probably  with  improved  details,  by  which  a  higher  per- 
centage strength  in  the  product  is  ensured. 
The  40  per  cent,  solution  of  formaldehyde,  as  met  with  in  com- 
merce, is  a  liquid  of  a  pale  sea-green  tint,  specific  gravity  about 
1-070,  acid  reaction,  and  possessing  a  pungent  and  very  characteris- 
tic odor.  In  more  concentrated  solutions  the  formaldehyde  tends 
to  pass  into  the  polymeric  and  comparatively  inactive  form  ;  this, 
therefore,  is  the  strongest  solution  which  will  remain  permanent. 
The  acidity  is  due  to  formic  and  acetic  acids,  and  the  faint  sea-green 
tint  to  a  salt  of  copper,  a  distinct  film  of  that  metal  being  deposited 
on  a  bright  steel  knife-blade  when  immersed  in  the  liquid  for  a  short 
time.  When  exposed  to  the  air,  formaldehyde  vapors  gradually 
diffuse,  and  the  solution  loses  strength. 
With  regard  to  the  toxicity  or  otherwise  of  formaldehyde  in  solu- 
tion, when  taken  internally,  no  record  of  exact  experiments  relating 
to  its  physiological  action  on  the  human  subject  appears  to  exist, 
and  information  such  as  we  possess  concerning  salicylic  acid,  car- 
bolic acid,  mercuric  chloride,  etc.,  is  wanting.    The  solid  polymer 
