240

DYEING AND CALICO PRINTING.

A hot deco&ion of sliced Levant madder-root is treated successively withneutral and basic acetate of lead. The second precipitate, after being tho-roughly washed, is decomposed with sulphuretted hydrogen. The sulphide oflead is well washed with cold water, which removes phosphoric and rubichloricacids, leaving almost the whole of the ruberythric acid along with the sulphideof lead. The lead compound is next thoroughly exhausted with boilingalcohol, and the solution thus obtained concentrated by evaporation on thewater-bath. The residue is taken up with water; a little baryta-water isadded, and the precipitate thus produced is filtered off. More baryta-water isadded, in order to throw down the ruberythric acid as a deep cherry-red floc-culent ruberythrate of baryta. This is dissolved in dilute acetic acid, thesolution nearly neutralised with ammonia, and then precipitated with basicacetate of lead. The cinnabar-red precipitate thus obtained is suspended inalcohol, decomposed with sulphuretted hydrogen, boiled, and filtered hot. Oncooling, ruberythric acid is deposited in bright yellow, silky, prismatic crystals.It is very soluble in ether, alcohol, and hot water, but sparingly in cold water.It bears, in many respedts, a great likeness to rubian. By mineral acids it issplit up into sugar and alizarin.

The researches of Kopp on the colourable glucosides are very interesting.*He treated Alsace madder, about six months old, with a saturated solution ofsulphurous acid. By this means the peculiar adlion of the ferment present inthe madder is arrested, and the colouring matters present are eliminated in asoluble condition. The filtrate is yellow, and on the addition of 2 to 3 percent of hydrochloric acid, and heating to 6o° C., a flocculent red matter isthrown down not containing a trace of alizarin. On raising the temperatureto the boiling-point alizarin is thrown down mixed with chlorrubin. Thealizaric glucoside is therefore more stable than the other glucosides. Theaqueous solution of madder, treated with dilute sulphurous acid, shows, afterpressure and filtration, the following properties:—The concentrated liquid isdeep orange, with a brownish shade. The taste is faintly acid, mixed with asweetish bitter. Notwithstanding the smell of the sulphurous acid, the cha-racteristic odour of madder is quite distinct. In closed vessels this solutionremains unaltered for a long time. Sometimes a brownish, light, flocculentdeposit forms. If the solution of sulphurous acid employed is contaminatedwith hydrochloric acid there is deposited, in five to eight days, a semi-crystalline mass of purpurin, of a bright vermillion-red. Since this depositis very heavy, it can easily be removed by decantation. If the fluid containingsulphurous acid is exposed to the air it loses its odour, and grows turbid. Apulverulent greyish-black substance is deposited, and the liquid becomes dis-coloured. Decomposition sets in, and when ammonia is added there is nolonger a beautiful violet-red, but a dirty muddy appearance. This solution ofmadder in sulphurous acid behaves with reagents as follows :—With potash,soda, and ammonia, no precipitate, but a violet-red colouration with a yellowishtinge. If the alkaline solutions are very concentrated a precipitate is formedon boiling. The liquid retains its original colour as produced by the additionof an alkali, and a portion of the precipitate is re-dissolved on the addition ofwater. Nothing is at first produced by the addition of hydrochloric acid, but

* E. Kopp, “ Repertoire de Chimie Appliquee,” tome Hi., p. 85, and “ Bulletin de la Soci6teIndustrielle,” tome xxxi., p. 145.