Am.  Jour.  Phariti.) 
October,  1911.  j 
Note  on  Assay  of  Formaldehyde, 
467 
be  the  most  generally  favored  and  that  it  is  the  official  method  of 
the  present  U.  S.  Pharmacopoeia.  We  may  therefore  •  ask,  What 
advantages  has  the  H0O2  method  over  other  methods,  such  as  the 
iodometric  or  Legler  method,  which  entitle  it  to  this  preference? 
The  answer  to  this  may  be  found  partly  in  the  results  of  Williams 
who  found  that  in  the  presence  of  small  amounts  of  ethyl  alcohol, 
paraldehyde,  methyl  alcohol,  or  acetone,  the  H2O2  method  gave 
normal  results  whereas  the  results  obtained  by  the  iodometric  method 
were  abnormal.  Similarly,  in  the  case  of  a  formaldehyde  solution 
which  contained  a  small  amount  of  acetaldehyde,  the  result  obtained 
by  the  Legler  method  was  47.8  per  cent,  instead  of  34.87  per  cent,  in 
the  absence  of  the  acetaldehyde,  thus  increasing  the  result  in  per- 
centage by  12.93;  whereas  by  the  H2O2  method,  under  similar  con- 
ditions, the  increase  in  the  percentage  was  only  2.78  (from  35.82  to 
38.6).  The  results  of  Williams,  however,  while  showing  that  the 
H2O2  method  is  more  advantageous  than  the  iodometric  or  Legler 
methods,  also  show  that  the  KCN  method  is  even  more  reliable 
than  the  H2O2  method.  For  not  only  were  the  results  by  the  KCN 
method  normal  in  all,  cases  where  the  H2O2  method  gave  normal 
results  but  even  in  the  presence  of  acetaldehyde  which,  as  already 
noted,  increased  the  results  by  the  H2O2  method  from  35.82  to 
38.6  per  cent.,  the  result  obtained  by  the  KCN  method  was  only 
slightly  higher  than  in  the  absence  of  the  acetaldehyde,  being  35.12 
per  cent,  in  the  absence  of  the  acetaldehyde  and  35.3  per  cent,  in  its 
presence;  while  according  to  Romijn very  exact  formaldehyde 
determinations  may  be  obtained  by  the  KCN  method  even  in  the 
presence  of  acetaldehyde,  acetone  or  benzaldehyde.  We  thus  see 
that  not  only  has  the  KCN  method  the  advantage  over  the  HgOo 
method  in  that  the  reaction  on  which  the  former  method  is  based  is 
characteristic  for  aldehyde  but  that  it  may  even  be  used  for  distin- 
guishing and  determining  formaldehyde  in  the  presence  of  certain 
other  aldehydes.  The  fact  also  that  in  the  JrLOo  method  the 
results  will  be  influenced  by  any  substance  which  on  oxidation,  under 
the  conditions  of  the  method,  will  produce  acid  products  capable  of 
consuming  a  portion  of  the  alkali  present,  has  led  Fresenius  and 
'"■'^Joiir.  Amcr.  Chem.  Soc.  600  (1905)- 
^^Zeit.  anal.  Chem.,  23,  22  (1897)  :  "Die  Cyaiikaliummethode  gestattet  also' 
auch  bei  Anwesenheit  von  Acetaldchyd,  beziehiingsweise  Aceton  oder  Benz- 
aldehyd,  eine  selir  gcnanc  Bestimmung  des  Formaldehyds." 
