The hydrochloride of methyl red is only sparingly soluble in cold water, and is apt to separate in blue needles if the acidity is not sufficiently reduced.
"Organic-Syntheses"
Conant, James Bryant
The free base is liberated by adding to the phenylhydrazine hydrochloride 1 l.
"Organic-Syntheses"
Conant, James Bryant
When this is done, no more phenylhydrazine hydrochloride is obtained by concentration of the mother liquor.
"Organic-Syntheses"
Conant, James Bryant