DIRECTOR   Agnes Bunting


Up to the present time there has been but one process for determining the value of a colouring matter. It consists in dyeing or printing with the different samples, and comparing the intensity of the shades produced. This method answers perfectly for industrial purposes. But there exists no chemical procedure for determining these bodies, and proving their purity. The author considers that he has effected this object with simplicity and precision, by making use of the power which hydrosulphite of soda possesses of reducing and decolourising different tinctorial bodies, and, amongst others, those derived from aniline. The apparatus employed is essentially the same as that which Schlitzenberger and Risler employ for the determination of oxygen dissolved in water. The hydrosulphite is drawn up by aspiration into a Mohr's burette. The solution to be titrated is poured into a small flask closed with a caoutchouc stopper, pierced with three holes. Through one of these passes the delivery-tube of the burette, whilst the other two serve for admitting into the flask a current of carbonic acid gas, since the experiments must be made in the absence of atmospheric air. Lastly, as the decolouration of these matters only takes place at 100°— except in case of magenta which is decolourised in the cold—the flask is placed on a sand-bath, and the contents kept at the boiling-point. If it is required, e.g., to analyse a sample of magenta, we weigh out 1 to 2 decigrammes, which are dissolved in water and diluted to a litre. At the same time a solution is prepared of 1 or 2 decigrms. of pure magenta in a litre of water. All that is required is to determine how many degrees of the hydrosulphite are required to decolourise each of these solutions. The ratio of the two numbers gives the value of the solution under examination. Other colouring matters have been titrated, and on comparing the results obtained it is found that 1 molecule of each of these different bodies whose composition is known requires for its decolouration the same quantity of hydrosulphite as would be consumed in reducing 2 molecules of ammoniacal sulphate of copper. This method offers another advantage—it < enables us to judge of the quantity of colouring matter ' contained in an unknown liquid. Itmaybealso used during the manufacture of aniline blues and violets to ascertain the amount of colouring matter which has been formed.