The aniline selected for this purpose should contain about 25% of the toluidine.
From this it will be evident that an aniline rich in toluidine is an essential condition for obtaining aniline red.
The large quantity of aniline and toluidine now made has opened up a channel for the use of the waste borings from cast-iron.
The result is a diazo-salt; aniline, for example, giving diazobenzene chloride, and toluidine diazotoluene chloride.
By a similar process toluene is converted into nitrotoluene, and the latter into toluidine.