Am.  Jour.  Pharm.  ) 
Sept.,  1921.  5 
Improved  Deniges  Test. 
633 
Purely  qualitative  findings,  however,  seldom  afford  solid  ground 
for  action  in  matters  of  commercial  or  legal  importance.  The  ques- 
tion "How  much  ?"  is  almost  certain  to  arise.  It  is  a  pertinent  ques- 
tion here,  inasmuch  as  several  investigators4  have  stated  that  meth- 
anol is  naturally  produced  in  certain  fermentations.  If  methanol, 
like  fusel  oil,  is  a  normal  constituent  of  alcoholic  products,  then  the 
legitimacy  of  its  presence  in  any  case  may  be  satisfactorily  settled 
only  by  quantitative  examination.  The  analytical  chemist  needs,  first, 
a  simple  but  dependable  qualitative  test  which  shall  possess  semi- 
quantitative value  in  that  it  is  able  to  serve  as  a  "limit  test,"  and, 
second,  a  quantitative  method  which  shall  enable  him  to  assert  with 
positiveness  very  nearly  the  exact  percentage  present.  The  quan- 
titative method  must  be  subjected  to  intensive  study  in  order: 
(1)  To  develop  its  highest  inherent  precision. 
(2)  To  devise  methods  for  the  elimination  of  interfering  sub- 
stances. 
(3)  In  case  elimination  is  impossible,  to  determine  the  size  of 
the  "blank"  involved  by  the  presence  of  each  such  substance. 
The  Deniges5  test  seems  most  promising  for  both  qualitative 
and  quantitative  application.  It  consists  in  treating  the  alcoholic 
solution  with  potassium  permanganate  and  acid,  whereby  methanol 
is  oxidized  to  formaldehyde.  The  latter  is  detected  by  Schiff's 
reagent  in  the  presence  of  sufficient  sulfuric  acid  to  prevent  develop- 
ment of  color  from  acetaldehyde.  There  appears  no  evidence  that 
other  proposed  oxidizing  agents,  such  as  bichromate  and  acid  or 
persulfates,6  are  inherently  superior  to  permanganate  and  acid.  The 
latter  agent  is  pre-eminently  simple  and  convenient,  requiring  no 
heat  for  its  action  and  finally  affording  a  colorless  solution.  No 
reagent  effects  a  quantitative  yield  of  formaldehyde.    All  require 
4  von  Fellenberg,  Mitt.  Lebensm.  Hyg.,  5  (1914),  172;  Biochem*  Z.,  85 
(1918),  45;  Takahashi,  /.  Coll.  Agr.  Imp.  Univ.  Tokyo,  5  (1915),  301;  /.  Am. 
Chem.  Soc,  39  (1917),  2721. 
6  Compi.  rend.,  150  (1910),  832. 
6  Preliminary  experiments  have  indicated  that  persulfates,  especially  in 
strongly  acid  solution,  may  produce  a  notable  quantity  of  formaldehyde  from 
pure  ethyl  alcohol.  The  possibility  of  such  a  reaction  has  been  noted  by  previ- 
ous observers  in  the  application  of  several  oxidizing  agents.  Bichromate  and 
acid,  in  comparison  with  permanganate  and  acid,  appears  to  afford  a  high  yield 
of  acetaldehyde  from  ethyl  alcohol,  but  a  low  yield  of  formaldehyde  from 
methanol. 
