596 
U,  S.  P.  Test  for  Methyl  Alcohol  {^i^'J^™- 
If  the  solutions  are  cooled  and  kept  cool  (24°-25°  C.)  during 
the  test  a  positive  color  reaction  is  obtained  provided  the  methyl 
alcohol  content  is  about  I  per  cent,  or  higher;  but  if  as  low  as 
0.25-0.5  per  cent,  the  appearance  of  the  color  may  require  from  fif- 
teen to  thirty  minutes,  depending  upon  the  kind  of  light  under  which 
it  is  viewed.  With  small  quantities  of  methyl  alcohol  the  appearance 
of  the  test  may  indicate  a  negative  reaction  even  after  fifteen  to 
twenty  minutes,  if  viewed  by  daylight.  This  is  due  to  a  mixture  of 
pale  tints  which  neutralize  each  other.  The  final  color  resulting 
when  ethyl  alcohol  is  tested  is  a  pale  yellow,  but  if  methyl  alcohol  is 
present  the  pale  violet  tint  which  would  otherwise  appear  is  masked 
by  the  yellow  and  the  solution  appears  to  be  colorless  when  viewed 
transversely  by  daylight,  but,  viewed  vertically,  with  the  light  from 
above,  it  gradually  changes  to  pale  greenish  and  finally  to  pale  blue 
or  violet.  When  the  same  test  is  observed  under  artificial  (yellow) 
light  the  contrast  is  striking ;  the  source  of  light  may  be  the  ordinary 
"  Mazda  "  or  the  carbon  filament  electric  bulb,  the  open-flame  gas 
burner  or  even  the  incandescent-mantle  gas  light.  Viewed  directly 
from  above  under  either  of  these  lights,  against  a  white  background, 
the  first  indication  of  the  presence  of  methyl  alcohol  is  a  faint  sal- 
mon-pink color  which  changes  to  violet-pink  then  cherry-red;  by 
reflected  artificial  light  the  color  is  a  rather  pale  violet ;  the  pink  to 
violet  may  be  pale  but  distinct  before  any  color  is  perceptible  by  day- 
light. These  colors  relate  to  small  quantities  of  methyl  alcohol 
(0.25-0.5  per  cent.)  and  require  ten  to  fifteen  minutes.  With  larger 
quantities  of  methyl  alcohol  (1  per  cent,  or  more)  the  question  of 
light  is  not  so  important,  the  first  color  being  violet  and  changing 
to  purplish  red  in  a  few  minutes  by  either  light.  Blank  tests  made 
on  pure  10  per  cent,  ethyl  alcohol  may  produce  at  first  a  pale  pink 
or  even  a  faint  violet  by  artificial  light,  but  if  the  temperature  has 
been  properly  controlled  these  fade  to  pale  yellow  in  ten  to  fifteen 
minutes. 
The  above  figures  are  approximate,  no  attempt  having  been 
made  to  determine  the  exact  range  of  temperature,  but  the  best  re- 
sults were  obtained  at  23°-25°  C.  The  time  required  for  the  ap- 
pearance of  a  decided  color  reaction  depends,  of  course,  upon  the 
amount  of  methyl  alcohol  present. 
Sodium  bisulphite  is  likely  to  be  met  with  which  has  a  yellowish 
color  and  the  fuchsin  reagent  in  which  it  is  used  may  be  sufficiently 
