Watery solution of iodine imparts to it a deep mahogany-brown colour; iodine and sulphuric acid occasionally, but not always, an azure-blue, methylviolet, a brilliant rose-pink and methyl-green gives a reaction very much like that of methyl-violet, but not so vivid.
Iodine gives usually a dark brown reaction, sometimes a deep blue; iodine and sulphuric acid almost always call forth an intense deep blue reaction; and methyl-violet usually a brilliant pink, quite resembling that of true amyloid.
Koch discovered that methyl violet dye showed up the septicaemia germ under a microscope by staining it.
