378

DYEING AND CALICO PRINTING.

dissolving tin crystals in double their weight of water, is then added, and thewhole is brought to a boil. A pure orchil gives only a faint yellowish colour.The presence of logwood is shown by a greyish-blue re'sidue, whilst sapan orpeach-wood is indicated by a reddish tinge. The adtual beauty and tone ofdifferent samples of orchil can only be ascertained by dyeing swatches ofsome suitable material—such as white camlet, French merino, or flannel—withequal weights of the samples under examination, under circumstances quitesimilar.

Orchil liquor is used in dyeing wool and slubbings which could not readilybe freed from fragments of the weed if the paste were employed. Liquorsrange in strength from 8° to 20° Tw. They are best tested by dyeing compa-rative samples.

Cudbear, in addition to salt, is sometimes adulterated with ground chalk.These impurities may be detected by burning a weighed quantity to ashes.If genuine, the residue will be inconsiderable. Or swatches of a whitewoollen or worsted material, equal in weight, are dyed with equal weights ofthe samples.

Since the year 1857, MM. Guinon, Marnas, and Bonnet have obtained fromlichens a product known as pourpre Frangaisc, which yields not only anextremely beautiful and brilliant but fast dye-material. This dye-material isprepared as follows :—The lichens are treated with a cold ammoniacal liquid,whereby the colourable acids are dissolved. After having been in contact withthis fluid only for a few minutes, the lichens are placed on a filter, in a bag,which is squeezed very strongly, the filtered liquid is precipitated with hydro-chloric acid, the ensuing precipitate is filtered, washed and left to drain, andnext dissolved in ammonia, and left exposed to the action of air in the cold.Up to this part of the proceedings there is no difference from the ordinarymethod of orchil making, but instead of allowing the process to go on untilthe peculiar colour of orchil is completely developed, the moment when theliquid mass becomes a cherry-red is watched, and, as soon as that point hasbeen reached, the material—semi-fluid, or thickish fluid—is brought to ebulli-tion, which is kept up for some time. It is then run into flat-bottomed, rathershallow vessels, of from 2 to 3 litres capacity each, so as to form layers offrom 3 to 6 centimetres in thickness: these vessels and contents are heatedto from 70° to 75°, in a properly construdled stove-room : the operation isfinished when the liquid has assumed a beautiful purple tint, and does not,when painted over a sheet of white paper, change its colour after drying.The purple matter thus obtained is accompanied by a red acid, which altersits beauty. In order to eliminate that acid chloride of calcium is added, whena precipitate, or lime lake, is obtained, which, after having been filtered,washed, and dried, appears a bluish-purple mass, and when rubbed with thefinger-nails assumes a cupreous hue. By fractional precipitation lakes ofdifferent shades are obtained. The mother-liquor retains, beside some of thepurple, a red substance, which may be applied to dye pomegranate-colour onsilk, and is also a fast colour.*

Instead of a lime lake an alumina lake may be prepared by employingalum for the precipitation of the ammoniacal solution. By treating the limelake of the pourpre Framjaise with an equivalent quantity of oxalic acid, and

* J. Pcrsoz, “ Report, de China. Appliq.,” vol. i., p. 1S9.