Re: methyl green is methyl blue

From:"J. A. Kiernan" <>

> kwalters <> wrote:
> Everytime I make methyl green it turns a gorgeous shade 
> of blue.  I have a brand new powder that I am using.

Methyl green manufactured during the last 20 years or so is
really a related dye called ethyl green (CI 42590), and it
should not contain crystal violet, the contaminant that
had to be extracted with chloroform from real methyl
green (CI 42585). At least one firm, Aldrich, has the dye
under ethyl green in the catalogue, but even they still
call it methyl green on the bottle!  Both dyes are a bluish
shade of green, and the Colour Index name for methyl green
is Basic blue 20!  Real methyl blue (CI 42780, Acid blue 93)
is different, being a strongly bright blue anionic dye that's
used for staining collagen in mixtures with other dyes that
stain other things.

It is just possible that your supplier is selling old (real) methyl 
green that contains crystal violet.  If that's what you've got
you'll have to shake the solution with chloroform in a separating 
funnel with repeated changes until the chloroform layer is no longer
violet. The solution is then stable for years. Otherwise cut your
losses and buy a "methyl green" that is fairly recently certified
by the Biological Stain Commission  _and_  is stated by the
supplier to be free of violet contaminants.  (In earlier times the
BSC approved methyl green that needed extracting, because
that was all there was.  See Lillie, 1977: Conn's Biological Stains
9th edn; Baltimore: Williams & Wilkins.)
John Kiernan
London, Canada.

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