Am.  Jour.  Pharm.  1 
February  ,  1898.  j 
Testing  of  Formaldehyde. 
95 
in  such  a  manner  as  experiments  seemed  to  show  most  practical. 
No  test  for  methyl  alcohol  is  included,  as  it  was  not  found  practi- 
cable to  test  for  it  in  presence  of  formaldehyde  except  by  tedious 
distillation.  The  pungent  odor  of  formaldehyde  completely  masks 
the  wintergreen  odor  obtained  by  the  salicylic  acid  test,  even  when 
a  large  quantity  of  methyl  alcohol  is  known  to  be  present. 
The  solution  should  contain  35  to  40  per  cent,  of  absolute  formal- 
dehyde, as  ascertained  by  the  ammonia  method  or  its  modification. 
It  should  be  transparent  and  colorless,  have  a  pungent  odor  and 
'  caustic  taste,  and  a  neutral  or  faintly  acid  reaction.  Specific  gravity 
about  1  08  at  I5°C.  Miscible  in  all  proportions  with  water  and  with 
alcohol.  On  mixing  with  an  ammoniacal  solution  of  silver  nitrate, 
metallic  silver  is  separated.  Heated  with  alkaline  copper  tartrate 
solution,  cuprous  oxide  is  separated. 
If  to  2  c.c.  of  the  solution  an  equal  volume  of  potassa  solution  and 
about  0-5  gramme  of  resorcinol  be  added  and  the  mixture  heated 
to  boiling,  the  yellow  color  which  first  appears  gradually  becomes 
red.    (This  reaction  is  said  to  be  given  by  no  other  substance.) 
If  5  c.c.  of  sulphuric  acid  (specific  gravity  1-34)  be  placed  in  a 
test-tube  with  a  little  salicylic  acid  and  2  drops  of  formaldehyde 
solution  added,  a  permanent  deep  red  color  will  appear  immediately. 
If  I  c.c.  of  the  solution  be  evaporated  to  dryness  on  a  water-bath 
after  addition  of  5  c.c.  of  ammonia  water,  a  white  crystalline  residue 
will  remain,  which,  upon  moistening  with  dilute  sulphuric  acid  and 
warming,  will  evolve  the  pungent  odor  of  the  original  solution.  (Re- 
conversion of  hexamethylene-tetramine  into  formaldehyde  and 
ammonia.) 
If  5  c.c.  be  evaporated  to  dryness  on  a  water-bath,  a  white  amor- 
phous mass  is  left,  which  should  leave  no  residue  on  ignition 
(absence  of  mineral  impurities). 
ft 
Ten  c.c.  should  require  not  more  than  0-25  c.c.  of  _  potassium 
hydrate  for  neutralization,  using  phenolphthalein  as  indicator 
(absence  of  more  than  o-i  per  cent,  of  formic  acid). 
A  coil  of  clean  platinum  wire,  dipped  into  the  solution  and  held 
into  a  non-luminous  flame,  should  not  color  the  flame  yellow 
(absence  of  sodium),  nor  should  it  appear  violet  when  viewed 
through  a  blue  glass  (absence  of  potassium). 
Dilute  the  solution  with  three  times  its  volume  of  water  for  the 
