A new diazotisable diamido-compound was obtained from this last hydrocarbon, and introduced in 1886 by Leonhardt & Co. One of the three isomeric nitrotoluenes furnishes a sulpho-acid which, on treatment with alkali, gives a compound derived from a hydrocarbon known as stilbene, and this, on reduction, is converted into the diamido-compound referred to. The latter, which is a disulpho-acid as well as a diamido-compound, can be diazotised and combined with phenols, &c. The stilbene azo-dyes thus prepared from phenol and salicylic acid, like the chrysamines, are yellow colouring-matters, containing two azo-groups. It is a valuable characteristic of these secondary azo-dyes that they all possess a special affinity for vegetable fibre, and their introduction has exerted a great influence upon the art of cotton-dyeing. We shall have to return to these cotton-dyes again shortly. Before leaving this branch of the subject, the following scheme is presented to show the relationships and inter-relationships of the products thus far dealt with in the present chapter-- Tar | --------------------------------------------------------- | | Light Oil Carbolic Oil / \ /-> Benzal Chloride | / \ / | \ | / \ / | Benzaldehyde | / \ / Cinnamic acid | | Benzene Toluene | Nitrobenzaldehyde | | | Nitrocinnamic acid (+ acetone) | | | | / | | | | / |-----------| Nitrobenzene Nitrotoluene Propiolic acid / | | | | \ | / Phenols Naphthalene | | \ | / | \ | | \ | / | \ | | \ | / | ->Cresols Azobenzene Azotoluene \ Indigo<--/ Phenol | | | Stilbene- | Victoria | | derivative <------------------- yellow | | (Diazotised)\ | \ Benzidine Tolidine Salicylic Picric Corallin \ / acid acid & Aurin (Diazotised) \/ --------------------------------