302

DYEING AND CALICO PRINTING .

colouring matter, the brilliancy and beauty of the shades produced are some-what impaired, whence this maximum of temperature is often avoided inpractice. It is of the very utmost importance to keep the temperature of thebath gradually and steadily rising, and to guard especially against a fall of theheat, which is invariably attended with great loss of colouring matter. Forinstance, if the temperature has been raised to 55 0 , then cooled down to 30',again heated up to 70°, next again cooled to 40°, and then brought up again toebullition, there will ensue a loss of 40 per cent. The explanation of thisphenomenon is not easy, but since this phenomenon is not observed with fleurde garance and garancin it is evident that the soluble constituents of themadder play an adtive part in the process going on in the dye-beck. Thesteeping of madder in water previous to use is injurious, and invariably givesrise to loss of colour, not because it is thereby destroyed, since it can evenresist fermentation and a far advanced stage of putrefadtion, but the colouringmatter becomes masked. When Avignon madder is thoroughly mixed witha quantity of ice-cold water at o° (32 0 F.) and the mixture filtered, a deepbrown filtrate is obtained, which, when heated in the usual manner, dyes apreviously mordanted piece of calico very well; but if this experiment be re-peated with water at 30°, the filtrate is quite clear and does not yield anydye. If Alsace madder is treated in the same way it yields at o° and at 30°solutions equally rich in colouring matter and fit for dyeing.

We quote here the results of some experiments made in this direction :—46 grms. each of the above kinds of madder were steeped for fifteen minutesin 32 times their weight of distilled water, and next filtered with the followingresults:—

Alsace madder,g grms. of the materialwere used.

5 grms. of the materialwere used.

At o° dyed as well as if

The residue on the filter

dyed as if.

Loss.

At 30° dyed as well as if

The residue on the filter

dyed as if.

Loss.

Avignon madder.

6 grms. of the materialwere used.

30 grms. were used.

10 grms.

1 grm. of the materialwas used.

28 grms. were used.

17 grms.

These figures can be interpreted in the following manner:—The colouringglucosides of the Avignon madder, which is neutral or alkaline, are, for a shorttime at least, not adted upon and preserved intadt at o°, but are rapidly splitup at 30° into an insoluble colouring matter; since Alsace madder is acid thisdecomposition is not so rapid, and consequently the phenomena produced areless sharply defined ; this observation applies to Zealand madder, which is alsoacid. If the question be asked, what quantity of madder or any of its com-mercial preparations should be used in the dye-beck, our answer is, that it isdifficult, if not impossible, to fix constant rules. Something depends uponthe greater or less fulness of the designs executed upon the cloth, upon thegreater or less degree of penetration of the mordant into the fibre, the greateror less perfedtion of the ageing and fixing, the perfection also of the originalbleaching of the cloth, and, lastly, the greater or less strength of the mordantsapplied. All these points influence the quantity of dye-stuff required. As a