APPENDIX.

685

37. Nitrous Derivatives of Resorcin.—By the adtion of nitrous acidupon resorcin Weselsky has obtained colouring matters which' in theirbrilliance and beauty rival the finest of the aniline colours, and which displayphenomena of fluorescence in a splendour far surpassing all bodies previouslyobserved. One of these compounds is formed by passing a current of nitrousacid into an ethereal solution of resorcin. It forms brown crystalline grainswith a green metallic lustre, sparingly soluble in water, and ra.ther moresoluble in alcohol and acetic acid. Its solutions are of a deep cherry-redcolour. In alkaline liquids it dissolves with a rich violet-blue. If the abovesubstance is treated with concentrated nitric acid, with the aid of heat weobtain nitrate of tetrazoresorcin in fine garnet-red crystalline needles of greatbrilliance. They dissolve in water, ether, and alcohol with a pure indigo-bluecolour. The discovery of a cheap source of resorcin is needed to render thesecolours pradtically available.

38. Cyanin.-—1 part of cinchonine or quinoidine is mixed with 3 parts ofhydrates of potash or soda, and as much water as would be needed to dissolvethe alkali with the aid of heat, and the mixture is distilled in an iron retort.Along with the watery vapours an oily liquid passes over and settles to thebottom of the water. This is crude chinoline, and amounts in quantity to65 per cent of the cinchonin used. After removal of the water the chinoline isredtified. The portion passing over between 216° to 360° C. is suitable for thepreparation of cyanin.

For a purple shade of cyanin 1 part of chinoline is mixed with i£ partsiodide of amyl. The mixture is brought to a boil, when it gradually takes adeep brown colour, and on cooling becomes a crystalline brown mass ofhydriodate of amyl-chinoline. The product of the readtion is boiled for tenminutes with six times its weight of water, and when dissolved the liquor isfiltered while still boiling.

The filtrate is placed in a boiler of enamelled iron, brought gradually to aboil, and mixed by degrees with an excess of ammonia. The boiling may bekept up for some hours with advantage, but the evaporated liquid must bereplaced with a mixture of equal parts of common ammonia and distilledwater. After boiling the mixture is allowed to cool, when the colouringmatter is almost entirely precipitated, the supernatant liquor retaining scarcelya trace of colour. The whole is then filtered to separate the colouring matter,which dissolves in alcohol with a fine blue purple colour.

To prepare cyanin the following process may be employed. The brownishblack crystalline mass above mentioned is moistened with five or six timesits weight of boiling water, boiled for some time, and filtered. Upon thefilter there remains a tarry mass, which dissolves in alcohol with a bright redcolour, and may be employed as magenta. The filtrate is of a yellowishgreen colour and milky appearance. It is heated to boiling and mixed witha lye of caustic soda or potash containing one-fifth of its weight of the solidalkaline hydrate. The lye is added by degrees to the liquid, which is kept ata gentle boil until a quantity of alkali has been introduced equivalent tothree-quarters of the iodine contained in the iodide of amyl employed. Afterboiling fifteen to thirty minutes, during which the liquid takes first a brickcolour and then a green, leaflets of a deep blue colour begin to fall, and uniteto a black resinous mass, which is cyanin. The colouring matter is filteredand washed with water, in which it is almost insoluble. If the filtrate is