396

DYEING AND CALICO PRINTING.

principles of this decoCtion are—(i) a peculiar tannic acid, called quercitannicacid , which colours the iron salts like ordinary tannic acid, but does not,like that acid, yield gallic acid ; (2) the quercitrin or aCtive principle.

In order to estimate the.tinctorial value of quercitron (or, as it is commonlycalled by dyers, “ bark”) a piece of previously mordanted cotton is dyed withthe ware to be tested, the operation being conducted as described undermadder, and the results compared with those obtained simultaneously with asample of quercitron known to be of good quality. A pale yellow colour ofthe quercitron may be taken as an indication of good quality. A few grammesof the sample may be burned off in a platinum crucible as a test for mineraladulterations, while the moisture also should be estimated by drying thesample at 120°.

Colouring Matters Contained in Quercitron.

1 part of quercitron boiled for a quarter of an hour with 10 parts of waterdeposits, after some days’ standing, a crystalline body, named quercitrin byM. Chevreul.* Dr. Bolley describes this principle as quercitric acid, and pre-pares it by exhausting the quercitron of commerce in a displacement apparatuswith alcohol at 84 per cent. The tannin (ordinary tannic acid) contained inthe solution is first removed by gelatin, and after filtration the solution isevaporated to dryness, yielding a crystalline mass, which is purified byseveral re-crystallisations from alcohol.f Some varieties of quercitron con-tain a substance soluble in cold water, and capable of being split up at 6o°, inthe presence of water, into sugar and quercitrin.

M. E. Schlumberger once accidentally when working upon such quercitronsucceeded in extracting quercitrin therefrom with the greatest ease by simplyheating to 6o° the cold aqueous infusion of the bark. The liquid when so heatedbecame turbid, and deposited the quercitrin in beautiful mother-of-pearl-likeshining crystals, which were nearly chemically pure. It rarely happens that thisphenomenon can be reproduced with the bark as imported; probably the resultwould be more satisfactory with the fresh bark, since it is not unlikely thatthe material known as flavin , and manufactured in the United States,although chiefly consisting of quercitrin, is produced by a similar processto that employed by M. Schlumberger. Any chemist desirous to preparequercitrin in quantity will do best to operate on flavin. It is onlynecessary to boil it with a large quantity of water, and to filter while boilinghot; the liquid on cooling deposits quercitrin. in a crystalline state, andalmost perfectly pure. Quercitrin is hardly soluble in cold water, but 25 partsof boiling water dissolve it; it is also soluble in alcohol, but not well inether. Ammonia and the aqueous solutions of caustic alkalies dissolvequercitrin readily, the colour of the solutions being a greenish yellow. Theammoniacal solution is rapidly oxidised by the action of air, and turns brown.Baryta water causes in the aqueous solution of quercitrin a reddish yellowprecipitate ; with alum solution a beautiful yellow colour is produced ; theacetates of lead and copper and the chloride of tin yield flocculent yellowprecipitates ; persulphate of iron turns the colour olive-green, and causes a

* Chevreul, “Lemons de Chimie Appliquee a ia Teinture, ” a valuable and now very rarebook; for years out of print.

t Bolley, il Annalen der Chemie und Pharmacie,” xxxvii., 101.