His perception of the analogy between it and ammonia led to his famous work on the amines and ammonium bases and the allied organic phosphorus compounds, while his researches on rosaniline, which he first prepared in 1858, formed the first of a series of investigations on colouring matters which only ended with quinoline red in 1887.
The constitution of the fuchsine bases (pararosaniline and rosaniline) was determined by E.
Rosenstiehl (Jahres., 1869, p. 693) found also that different rosanilines were obtained according to whether orthoor para-toluidine was oxidized with aniline; and he gave the name rosaniline to the one obtained from aniline and ortho-toluidine, reserving the term pararosaniline for the other.
A similar series of reactions was carried out with rosaniline, which was shown to be the corresponding derivative of tolyldiphenylmethane.
The free pararosaniline, C19H19N30, and rosaniline, C20H21N30, may be obtained by precipitating solutions of their salts with a caustic alkali, colourless precipitates being obtained, which crystallize from hot water in the form of needles or plates.
Many derivatives of pararosaniline and rosaniline are known, in which the hydrogen atoms of the amino groups are replaced by alkyl groups; this has the effect of producing a blue or violet shade, which becomes deeper as the number of groups increases (see Dyeing).