32

DYEING AND CALICO PRINTING.

by the ether was treated with cold alcohol, which dissolved the greatest partof it. The dark brown solution., after being filtered from a small quantity ofcolouring matter B, which was usually present, was evaporated to dryness,when it left a dark brown, shining, resin-like residue, consisting of thecolouring matter A.

The greatest part of the precipitate produced by acid in an alkaline extradof cotton is insoluble in alcohol. This portion, when dry, has the appearanceof a brown, friable, earthy mass, among which cotton filaments, particles ofwoody fibre, and other impurities derived from the cotton may be seen.When burnt it leaves a considerable quantity of ash. Its weight, when dry,amounted, in the case of East Indian cotton, to 77 per cent of that of theentire precipitate, in that of American cotton to 66 per cent. Though muchlighter in colour than the precipitate before treatment with alcohol, it stillcontains a quantity of colouring matter, which cannot be extraded by meansof boiling alcohol, not even when ammonia is added—a circumstance whichis due either to the presence of some colouring matter distind from those justreferred to, or perhaps to the latter being intimately combined with, or firmlyattached to, some other constituent of the mass. Dr. Schunck supposes thatit contains also a small quantity of some albuminous substance, the presenceof some such substance being rendered probable by an examination of theproduds of decomposition with caustic alkali, as will be explained presently.Its chief constituent, however, is a body belonging to the pedine class,generally either pedic or parapedic acid, or a mixture of both. The presenceof some such body is indicated by the gelatinous appearance of the precipitatewith acid, its increasing in bulk and partially dissolving in water after theprecipitating acid has been removed, and its shrinking and curdling on therenewed addition of acid or of salts or alcohol. Nevertheless the isolationand preparation, in a state of purity, of this substance cannot be effededwithout considerable difficulty, in consequence of the pertinacity with whichthe colouring matter adheres to and accompanies it. If the precipitate, afterexhaustion with boiling alcohol, is treated with boiling water, the latterdissolves a considerable quantity of the body in question, but on evaporationit leaves a dark brown residue, which, on analysis, is found to contain no in-considerable amount of nitrogen, a proof of the presence of one or both ofthe colouring matters of cotton. Dr. Schunck was unsuccessful in hisattempts to remove this impurity by means of animal charcoal, earths,metallic oxides, or salts of any kind. He succeeded, however, in devisingtwo methods of preparing, in a state of tolerable purity, a body soluble inwater having the properties and composition of Fremy’s parapedic acid, andthus proving that cotton contains a substance belonging to the pedine series.He was unable to procure pedine itself, though there can be little doubt thatit is pedine which exists originally in the fibre and gives rise to the formationof the pedic and parapedic acids which are contained in the alkalineextrad. One of the methods employed for preparing this acid, founded onthe insolubility of its alkaline compounds or salts in an excess of causticalkali, was as follows:—

The precipitate from the alkaline extrad of cotton, after exhaustion withboiling alcohol, was, without being previously dried, dissolved in dilute causticsoda-lye. The solution, after being filtered in order to separate the filamentsof cotton and other impurities which were present, was mixed with alcohol,