chromogenn.

1858 J. L. W. Thudichum Treat. Pathol. Urine 328 The chromogen of indigoferous plants is a peculiar colourless substance.

1879 H. Watts Dict. Chem. VIII. i. 696 The compound which requires only the presence of a salt-forming group to convert it into a dye-stuff may be called a chromogen (thus NO₂ is the chromophore of nitraniline and nitrophenol, and nitrobenzene is their chromogen).

1882 New Sydenham Soc. Lexicon Chromogen, a former term for a supposed vegetable colouring matter which is acted upon by acids and alkalis in producing red, yellow, or green tints.

1892 Dyer 20 June 92/2 Chromogen may even be used with other dyestuffs to obtain a variety of useful shades of brown.

1910 Encycl. Brit. VIII. 746/1 Other acid colours, e.g. Chromotrope, Chrome Brown, Chromogen, Alizarin Yellow, &c.

1961 H. Blackshaw & R. Brightman Dict. Dyeing 43 Chromogen, the whole atomic grouping of which the Chromophore and the Auxochrome(s) are a part.

1884 E. Klein Micro-org. vii. 41 Chromogenic micrococci..are characterised by their power of forming pigment of various colours.

1901 Lancet 6 July 41/1 Organic colourings..may be the product of certain species of bacteria. Hence they are called chromogenic bacteria.

1913 W. Bateson Mendel's Princ. Heredity (new ed.) viii. 142 All that is common to them [sc. albinos] is the absence of colour, i.e...of the chromogenic substance.