412

DYEING AND CALICO PRINTING.

alkaline earths redden it, and cause a precipitate; tin crystals and acetate oflead yield orange precipitates; acetate of copper a chestnut red-brown pre-cipitate; acids turn the colour a greenish yellow. Fustet is chiefly used fordyeing wool and some kinds of skins, and is also, though rarely, used as atanning material. With aluminous mordants it yields an orange-yellow colour,and with tin mordants an orange-red. These colours are, however, fugitive,and are altered by the adtion of alkalies and soap ; fustet is not applied incalico printing, and very little in cotton dyeing.

Colouring Matter from Buckwheat (Polygonum Fagopyrum).*

Dr. Schunck has extracted from the leaves of this plant a yellow crystallinecolouring matter, sparingly soluble in cold, more readily so in hot, water;readily soluble in alcohol, concentrated sulphuric and hydrochloric acids, and inalkalies. According to the author, the formula of this substance is CrjHeoOio,and he considers it identical with rutin, and also with the ilixanthin (obtainedfrom the leaves of the holly, Ilex aquifolium). The aqueous solutions of thissubstance yield, on the addition of acetate of alumina and acetate of lead,yellow precipitates ; with acetate of copper a greenish yellow; and with per-chloride of iron an olive-brown precipitate ; this dye yields, on previouslymordanted cotton, bright yellow shades. The pure dye is obtained by makinga decodtion of the leaves, to which while boiling a small proportion of asolution of acetate of lead is added, in order to precipitate thereby some othervegetable principles; the liquid is filtered while still boiling; hot acetic acidis next added, whereupon the pure material is deposited in the shape of smallacicular crystals.f The bark and root of the pomegranate contain besidetannin a yellow colouring matter, which has not been hitherto scientificallyinvestigated, but which, judging from its behaviour in dyeing, approaches toquercitrin and quercetin. It is used by dyers to a small extent for certainshades of drab and grey. The husk or rind of the pomegranate fruit is rarelyused in this country as a source of tannin, though it contains upwards of30 per cent of tannic acid, and it yields with iron mordants rich, bloomy blacks,and is used in Spain in preference to sumach both for dyeing and tanning. Asregards the use made in dyeing and printing of the yellow colouring mattersbelonging to the quercetric group, it is evident that the great analogy inproperties, composition, and chemical behaviour of these principles mustextend to their application as dye materials, but although this is actually so,it is not in pradtice indifferent whether the one or the other be used, and thisis chiefly due to the fad! that the pradtical dyer does not employ the puretindlorial principles, but either the vegetable matter in its native state oraqueous extradts, which are complex substances containing impurities, whichin various ways affedt the applicability of the dyeing process.

The following is the general outline of the use of these colours :—None ofthem can be fixed without the aid of a mordant whatever may be the natureof the fibre. With aluminous or tin mordants the tissues are dyed yellow,orange-yellow, or nankin-yellow, according to the strength of the mordant.With iron the shades obtained vary from grey to olive-green or black. Withmixed iron and alumina mordants olive and reseda-yellow colours are

* “ Dlngler’s “ Polytechn. Journal, 11 cxv., 157,

t “ Repertoire de Chimie Pure," i., p. 438. “ Chemical Gazette,” Nos. 399 and 201.