oSoberi9^2a''°'  }        Estimation  of  Methyl  Alcohol.  725 
method  had  therefore  to  be  employed.  This  consisted  in  treating  a 
persulphate  solution  with  an  excess  of  the  mixture  of  alcohols,  and 
examining  the  products  produced  in  the  initial  stage  of  oxidation. 
It  was  then  found  that,  under  conditions  such  as  these,  the  larger 
the  amount  of  methyl  alcohol  present,  the  greater  the  amount  of 
formaldehyde  present,  when  the  limited  amount  of  persulphate  used 
was  entirely  decomposed.  The  amount  of  formaldehyde  produced 
under  the  conditions  of  the  experiment  could  then  be  estimated  colori- 
metrically.  The  estimations  were  carried  out  as  follows:  Ten 
Cc.  of  the  ethyl  alcohol  containing  methyl  alcohol  are  diluted  with 
50  Cc.  of  water.  Five  Cc.  of  this  are  then  mixed  with  5  Cc.  of  a  i 
per  cent,  solution  of  ammonium  persulphate  in  a  test-tube;  this  is 
provided  with  a  short  air  condenser  and  heated  in  a  boiling  water 
bath  for  ten  minutes.  At  the  end  of  this  period,  i  Cc.  of  the  mix- 
ture is  added  to  i  Cc.  of  a  i  per  cent,  solution  of  phenyl  hydrazine 
hydrochloride,  with  which  it  is  heated  in  a  boiling  water  hath  for  five 
minutes.  After  cooling,  i  Cc.  of  a  2.5  per  cent,  solution  of  potassium 
ferricyanide  is  added,  and  then  3  Cc.  of  concentrated  hydrochloric 
acid.  A  pink  color  is  thereby  produced  when  methyl  alcohol  is 
present,  which  can  be  compared  with  the  colors  produced  in  a 
similar  way  from  samples  of  ethyl  alcohol  containing  known  amounts 
of  methyl  alcohol.  Experiments  have  been  carried  out  with  mix- 
tures of  ethyl  alcohol  and  methyl  alcohol,  when  the  latter  varied 
from  0.5  to  5  per  cent.,  and  it  is  possible  by  this  rough  comparison 
to  estimate  the  percentage  of  methyl  alcohol  when  contained  within 
these  limits  to  within  i  per  cent.  A  more  accurate  estimation  can 
be  obtained  when  a  colorimeter  is  employed.  The  method  of  carry- 
ing out  the  more  accurate  determination  is  described  below. 
It  will  be  noticed,  in  the  directions  given  above,  that  the  reaction 
mixture  is  heated  with  the  solution  of  phenylhydrazine  hydrochloride 
before  the  other  reagents  are  added,  when  carrying  out  the  test  for 
formaldehyde.  The  reason  of  this  is  that  during  the  reaction  certain 
quantities  of  the  ethylal  HCH(OC2H5)2,  and  probably  of  the  methylal 
HCH(OCH3)2,  are  formed  during  the  heating,  and  the  full  pink  color 
is  not  given  by  formaldehyde  combined  in  these  ways,  unless  the 
mixture  is  heated  with  the  solution  of  phenyl  hydrazine  hydrochloride 
before  adding  the  other  reagents.    (Compare  Schryver,  Loc.  cit.) 
In  carrying  out  the  more  accurate  colorimetric  estimations,  the 
pink  test  solutions  prepared  by  the  method  described  above  were 
diluted  with  70  Cc.  of  water,  and  the  color  was  then  compared  with  a 
