The portion distilling at about 200° C. is then methylated by means of methyl alcohol and methyl iodide at loo-i io C., the excess of methyl alcohol removed and the product obtained decolorized by sulphuric acid.
An aqueous solu tion of fuchsine is decolorized on the addition of sulphurous acid, the easily soluble fuchsine sulphurous acid being formed.
The residue is then dissolved in water, decolorized by animal charcoal and saturated at 50 C. with oxalic acid.
The precipitate is dissolved in boiling water, decolorized by potassium permanganate and decomposed by barium carbonate.
Excess of stain is afterwards removed from the tissues by the use of decolorizing agents, such as acids of varying strength and concentration, alcohol, &c. Different bacteria behave very differently to stains; some take them up rapidly, others slowly, some resist decolorization, others are easily decolorized.