AmseJp0tur'i92iarra'}  Improved  Deniges  Test.  635 
Dilute  the  solution,  previously  purified  as  necessary,  to  1  per 
cent,  by  volume  of  total  alcohol  (Sample  Solution  A).  Of  this, 
pipet  10  cc.  into  a  50-cc.  volumetric  flask,  add  10  cc.  of  a  4  volume- 
per  cent,  solution  of  pure  ethyl  alcohol,  and  make  to  the  mark  with 
water  (Sample  Solution  B).  Of  the  latter,  likewise,  dilute  10  cc. 
plus  10  cc.  of  the  4  per  cent,  ethyl  alcohol  to  50  cc.  (Sample  Solu- 
tion C).  Into  50-cc.  tall-form  Nessler  tubes  pipet  4  cc.  of  the 
three  sample  solutions.  Prepare  standard  methanol  tubes  contain- 
ing, respectively,  1,  2  and  3  cc.  of  a  0.04  volume-per  cent,  aqueous 
solution  of  pure  methanol  plus  1  cc.  of  4  per  cent,  pure  ethyl  alcohol, 
plus  sufficient  water  to  make  4  cc.  After  the  tubes  are  properly 
arranged  in  a  rack  the  following  operations  are  put  through  in  strict 
parallelism  remembering  that  each  reagent  is  to  be  added  to  all 
tubes  before  any  are  mixed: 
1 —  Add  1  cc.  of  a  1  in  5  volume  solution  of  phosphoric  acid 
(C.  P.,  85  per  cent.),  and  mix. 
2 —  Add  2  cc.  of  3  per  cent,  potassium  permanganate  solution, 
mix,  and  let  stand  30  min. 
3 —  Add  1  cc.  of  10  per  cent,  oxalic  acid  solution,  mix,  and  let 
stand  till  a  clear  brown  (about  2  min.). 
4 —  Add  1  cc.  concentrated  H2S04  (C.  P.),  mix,  and  let  stand 
a  few  minutes  for  temperatures  to  become  equal. 
5 —  Add  5  cc.  SchrfT-Elvove  reagent,  mix  well,  and  let  stand 
till  colors  are  sufficiently  developed  (0.5  to  2  hrs.). 
Each  1  cc.  of  the  0.04  per  cent,  methanol  in  the  standard  tubes 
is  equivalent  to  volume  percentages  of  methanol  in  total  alcohol 
contained  in  the  sample  as  follows: 
Sample 
Solution  Per  Cent. 
A  1 
B  5  * 
C  25 
For  more  precise  results  the  determination  is  repeated  on  the 
appropriate  sample  solution  with  more  closely  set  standards.  The 
sharpest  results  are  obtained  with  standard  tubes  containing  not 
over  1  cc.  of  standard  methanol.  To  bring  the  sample  into  this 
range  it  is  often  best  to  use  only  2  cc.  of  a  sample  solution,  adding 
