456  Note  on  Assay  of  Formaldehyde.       {^^6ctdblx  im*' 
dation  and  condensation  methods  and  the  possible  incompleteness 
of  the  condensation  reactions. 
The  methods  investigated  by  Williams  were  those  which  are 
most  generally  recommended  for  the  determination  of  formalde- 
hyde, namely,  the  ammonia  method  of  Legler,^  the  hydrogen  peroxide 
method  of  Blank  and  Finkenbeiner/  and  the  iodometric  and  potas- 
sium cyanide  methods  of  Romijn.^  His  conclusion  that  the  results 
obtained  by  the  condensation  methods  are  lower  than  those  obtained 
by  the  oxidation  methods,  is  in  harmony  with  the  previous  work 
of  Smith, *^  who  also  found  that,  as  compared  with  the  Legler 
method,  "  the  hydrogen  peroxide  method  almost  invariably  gave 
higher  results."  Smith  also  seems  to  hold  the  view  that  the  potas- 
sium cyanide  method  is  applicable  to  dilute  solutions  only,  since  he 
refers  to  the  KCN  method  as  a  "  method  w^hich  is  applicable  tO'  solu- 
tions containing  but  small  quantities  of  formaldehyde ;  "  and  while 
he  concludes  that  "  the  iodometric  and  potassium  cyanide  methods 
give  good  results  on  dilute  solutions,"  he  adds  that  "  it  should  be 
remembered  that  in  diluting  strong  solutions  to  the  range  of  these 
methods,  a  small  error  in  weighing  may  be  considerably  multiplied." 
Apparently  influenced  by  this  suggestion  of  Smith,  many  authors 
on  analytical  chemistry  do  not  recommend  the  potassium  cyanide 
method  except  in  the  case  of  dilute  solutions.  Thus  Leffmann  and 
Beam,'''  referring  to  the  work  of  Smith,  state  that  for  the  determina- 
tion of  formaldehyde  the  choice  of  the  method  "  will  depend  on  the 
strength  of  the  solution,"  recommending  the  iodine  method  of  Romijn 
in  the  case  of  moderately  strong  solutions  and  the  potassium 
cyanide  method  for  dilute  solutions.  Likewise,  from  Schimpf,^ 
who  also  refers  to  the  work  of  Smith,  one  gains  the  information 
that  "  the  Blank  and  Finkenbeiner  method  is  very  satisfactory  for 
strong  solutions  "  and  "  the  iodometric  and  potassium  cyanide 
methods  give  good  results  on  dilute  solutions."  Similarly,  Leach  ^ 
omits  the  potassium  cyanide  method  as  a  suitable  method  for  deter- 
mining formaldehyde  in  the  commercial  preservative,  although  list- 
'Ber.,  i6,  im-iZ2>7  (1883). 
^  Ber.,  31,  2979-2981  (1898). 
Zeit.  anal.  Chern.,  36,  18-24  (1897). 
Jour.  Amer.  Chem.  Soc,  25,  1028-1035  (1903). 
'Leffmann  and  Beam:  Food  Analysis,  2d  ed.,  p.  84  (1905). 
"Schimpf:  Manual  of  Volumetric  Analysis,  5th  ed.,  pp.  644-645  (1909). 
"Leach:  Food  Inspection  and  Analysis,  2d  ed.,  p.  819  (1907). 
