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DYEING AND CALICO PRINTING .

reddened by the acidity of the vegetable juice ; and lastly, two yellow principles,viz., xanthin, insoluble in water, and xanthein, soluble therein.

Cyanin is best prepared from the petals of the violet or iris (Florentine),by exhaustion with boiling alcohol, when the petals become decolourised andthe liquid assumes a beautiful blue tint. This alcoholic solution turns rapidlyto a yellowish-brown, in consequence of a reduction which takes place, butwhen the liquid is agitated in contact with air the original colour is restored.This reaction cannot be often repeated without causing the destruction of thecyanin. The alcoholic liquid (solution of impure cyanin) is therefore evapo-rated to dryness on the water-bath, and the residue is taken up with water,which dissolves the blue colour, leaving resinous and fatty matters untouched.The aqueous solution is precipitated by neutral acetate of lead, and the beau-tiful green precipitate is, after having been well washed with distilled water,decomposed by means of sulphuretted hydrogen ; the liquid freed from sul-phide of lead by filtration is again evaporated to dryness, the residue taken upwith absolute alcohol, and the cyanin precipitated by means of ether.Cyanin thus prepared is a non-crystallisable solid substance, soluble inalcohol and water, insoluble in ether: acids, even if very weak, turn this sub-stance red, while alkalies render it green ; reducing agents decolourise it,but oxygen restores the colour.

The red colouring matter of flowers is extracted from the petals by a methodsimilar to that just described, and the material obtained exhibits all the cha-racteristic properties of cyanin.

According to MM. Cloez and Fremy, the petals of red or rose-red flowersare acid, while those of blue flowers are neutral. Some red flowers assume,while fading, first a blue and next a green colour: this appears to be due tothe partial decomposition of a nitrogenous principle, whereby traces of am-monia are set free ; other flowers, on the contrary, change from violet to red;a very rapid drying of red, pink, or rose-red flowers, whereby the carbonicacid contained in some of them is eliminated, may cause the colours tobecome blue. The rose-red, pink, violet, and blue colours of flowers seemtherefore due to the same substance, the differences of hues being broughtabout by a difference in the quality of the vegetable juice. Scarlet flowers,and such as exhibit a high red tint, are assumed to contain cyanin, mixedwith yellow matters. Some red flowers, those of the aloe species especially,do not contain cyanin, but instead thereof a peculiar substance, which ishardly soluble in water, insoluble in ether, but soluble in alcohol, and not aCtedupon, not turned to any other hue of colour, by either acids or bases.

Cyanin appears to be related to the roseo-cyanin formed by the aCtion ofboric acid upon curcumin, the colouring principle of turmeric. Both sub-stances are very unstable, and the reactions they exhibit are very similar.The paracarthamin obtained by Dr. Stein, by the action of sodium amalgamupon a mixture of quercetin and meletin, is also in its characters analogousto cyanin.

Colouring Matters of the Malvaceae.

The petals of the plant known as Altluza rosea> belonging to the naturalorder Malvaceae, contain a peculiar colouring matter, soluble in water andalcohol, but insoluble in ether. The aqueous solutions of the petals, freed pre-viously from the calix and stamens, exhibits a violet-red colour, which is turned