4^8  A^otc  on  Assay  of  fonualdehyde.       {^"october  Sii'^'"' 
Griinhut  ~^  to  recommend  that  in  assaying  commercial  formalde- 
hyde by  the  H2O2  method  the  results  obtained  should  be  confirmed 
by  the  iodometric  method,  since  ,it  is  only  when  both  methods  give 
closely  agreeing  results  that  the  mean  of  the  two  may  be  taken  to 
represent  the  actual  amount  of  formaldehyde  in  the  solution. 
But  these  are  not  the  only  disadvantages  of  the  H2O2  method. 
For  according  to  Smith,-^  the  working  range "  of  the  H2O2 
method,  on  the  lower  end,  ends  with  solutions  containing  about  5 
per  cent.  HCHO ;  so  that  when  we  have  occasion  to  carry  out  com- 
parative experiments  requiring  a  knowledge  of  the  formaldehyde 
content  of  the  strong  solutions  and  also  of  solutions  which  contain 
considerably  less  than  about  5  per  cent,  formaldehyde,  if  we  would 
use  the  Yi^O.^  method  we  would  be  obliged  to  use  two  dififerent 
methods  in  the  same  work.  Therefore,  should  we  not  prefer  a 
method  (the  KCN  method)  which  can  be  universally  applied  to 
formaldehyde  solutions,  whether  these  be  strong  or  weak  with  refer- 
ence to  their  formaldehyde  content,  and  which  is  based  on  a  reac- 
tion that  is  characteristic  of  aldehyde  and  also  permits  of  distinguish- 
ing and  estimating  formaldehyde  in  the  presence  of  certain  other 
aldehydes?  Finally,  we  may  add  that  the  KCN  method  has  also 
the  advantage  of  being  based  ultimately  on  the  beautiful  and  exact 
Volhard  thiocyanate  method  and  that  the  silver  nitrate  solution 
required  comes  nearest  to  the  chosen  ultimate  standard  for  volu- 
metric solutions — pure  metallic  silver.-*^ 
In  connection  with  the  study  of  embalming  fluids  to  which 
reference  has  already  been  made  above,  it  was  desired  also  to  obtain 
Zeit.  anal.  Chcm.,  44,  15-16  (1905):  "  Wir  sind  immer  dafiir  einge- 
treten,  diese  beiden  Arbeitsweisen  bei  der  Handelsanalyse,  insbesondere  bei 
der  Schiedsanalyse,  neben  einander  zu  benutzen  und  das  Mittel  der  nach 
beiden  Verfahren  erhaltenen  und  hinreichend  ubereinstimmenden  Werte  als 
den  wahren  Formaldehyd  gehalt  anzusehen.  Diese  Forderung,  zwei  verschie- 
dene  Methoden  anzuwenden,  bernht  daraiif,  dass  beide  nicht  eigentlich  auf 
die  directe  Bestimmung  des  Formaldehyds  abzielen,  ihn  also  nicht  in  einer 
wohlcharacterisierten  und  leicht  zu  identifizierenden  Verbindungsform 
abscheiden.  Beide  benutzen  viel  mehr  Reactionen,  die  ausser  dem  Formalde- 
hyd noch  sehr  viele  andere  Verbindungen  zeigen  konnen :  die  eine  lasst  alle 
Substanzen  finden,  die  in  alkalischer  Losung  durch  Wasserstoffsupero'xyd  zu 
Sauren  oxydiert  werden,  die  andere  alle  die  jenigen,  die  in  alkalischer 
Losung  durch  Jod  oxydiert  werden  oder  in  anderer  Weise  Jod  verbrauchcn, 
ohne  es  beim  Ansauren  wieder  frei  zu  geben." 
'^^  Jour.  Amer.  Chem.  Soc,  25,  1034  (1903)- 
'"'Elvove:  Amer.  Jour.  Pharm.,  82,  203-211  (1910) 
