74

DYEING AND CALICO PRINTING.

in a pure state they do not appear to be at all soluble in pure water. Underthe combined influence of heat and moisture, or of mineral acids and somemetallic salts and organic compounds, these substances are converted intoallotropic modifications, whereby they become insoluble. Albumenoid sub-stances, as a rule, are not soluble in alcohol, ether, or neutral organic liquids.Exposed to a high temperature (that is to say, below red heat), these com-pounds become decomposed, swell up, and fuse, yielding on dry or destructivedistillation a very large number of rather complex compounds according tothe degree of heat applied. Among these products we find sulphurettedhydrogen gas and hydrosulphide of ammonium, ammonia, carbonate ofammonia, aniline, picoline, pyridine, toluidine, pyrrol, methylamine, propyl-amine, and. tetrylamine. A portion of the nitrogen combines intimately withthe carbon, yielding a nitride of carbon formerly employed in the manufactureof cyanides. Water, carbonic acid, neutral oxygenated principles, and hydro-carbons are simultaneously formed.

Albumenoid substances are more or less readily soluble in weak aqueoussolutions of caustic alkalies. The quantity of caustic alkali should be verysmall, for if the solution be even as weak as 2 per cent of solid hydrate, adecomposition of the albumenoid matter ensues in most cases, and minutequantities of sulphuretted hydrogen are given off. These solutions are pre-cipitated by acids, but the precipitate does not necessarily reconstitute theidentical substance. When heat and stronger alkaline solutions are simul-taneously applied, ammonia, organic alkalies, carbonic and formic acids,leucine, tyrosine, gelatine, and sugar are generated. When these substancesare fused with alkalies, an alkaline cyanide is obtained. The albumenoid,called also protein, substances combine with both acids and alkalies, yielding,with the former, compounds which are insoluble in acidulated water, butsoluble in pure water.

Concentrated acetic and other organic acids, and the hydrate of the tribasicphosphoric acid dissolve albuminous substances; these solutions are pre-cipitated by an aqueous solution of ferrocyanide of potassium, which doesnot precipitate the solutions in these same acids of gelatine and gelatine-yielding tissues. Concentrated hydrochloric acid aided by heat yields withthe albumenoid substances, provided air be admitted, a solution whichassumes a rich blue-purple colour. Nitric acid has the effedt of colouring thesesubstances deep yellow, owing to the formation of xanthoproteic acid, which,on the addition of ammonia, assumes an intense orange colour. This propertyof nitric acid is turned to account in the production of beautiful and fastyellow and orange colours in woollen and silken fabrics and in feathers. Asolution of mercury in nitric acid (1 part of metal and 2 of nitric acid at 36° B.)yields, when heat is applied, an intensely red colour with all albumenoid sub-stances. These bodies are coloured deep brown with iodine. Strongoxidising agents, such as chromic and permanganic acids, and a mixture ofsulphuric acid and peroxide of manganese, adt very energetically upon thealbumenoid substances, producing a great many homologues of the fatty acidseries (Ch.H 2K 0 2 ) and the corresponding aldehydes; also benzoic acid, hydruretof benzoyl, hydrocyanic acid, and the cyanides of methyl, ethyl, &c.

Ozone also adts upon some of these substances in a peculiar manner. Whenalbumenoid substances come into contadt with air and moisture at a sufficiently