3°4

DYEING AND CALICO PRINTING.

only a small quantity of calcareous matters, alkalies or chalk may be withinreasonable limits advantageously added to the contents of the dye-beck. Asregards the first-named kind, it is a known fact that it will not produce fastcolours without this addition.

As to the part played by chalk in madder dyeing, there can be no questionwhatever about the advantage resulting from its addition, since on this pointthe comparative experiments made by M. H. Schlumberger with Alsacemadder, with or without chalk, and with Avignon madder, which is naturallyrich in lime compounds, are incontestible. Zealand madder has been ex-perimented with some years ago, comparatively with Avignon madder in asimilar manner, by a committee of practical and scientific men,* care beingtaken (a matter of importance in such trials) to use madder of the same ageand maturity in both instances, while the water used was either distilled orwater the solid contents of which were perfectly known. The results ob-tained on the large scale have proved that Zealand madder of proper maturitydoes not absolutely require the addition of chalk, but with that addition theshades produced are superior, the mordants and all conditions being alike,to those yielded by Avignon madder or any other. This fadt has also beenobserved by Prof. Girardin, who along with very many in France regret that,in order to please the Vaucluse madder growers, Zealand madder is practicallyprohibited from importation by an enormously high rate of duty. As to themode of action of chalk, this may be either simply for saturating the acidityof the madder, or it may actually enter into the lake to be produced, and thusrender the colours fast. We have already said that Alsace madder does notyield shades which stand clearing well unless chalk has been added. If thesaturation of the acid were the only object, it is quite clear that the precisequantity required for neutralisation of the acid would suffice, but this hypothesisis not in accordance with the aCtual results obtained by experience on the largescale, which have conclusively taught that an excess of chalk is absolutelynecessary. Experiments made by M. D. Kcechlin many years ago proved thatdyeing operations made with a binary mordant give rise to the production offaster colours than when only a single mordant is used. M. H. Schlumberger’sopinion on this point is, that the chalk becomes fixed on the mordantedportions, producing a binary compound of greater stability than that of thealuminous substance by itself only.

The following may illustrate the meaning here briefly expressed:—Whena piece of cloth is first mordanted with a preparation of binoxide of tin, nextwith an aluminous mordant, and next treated with an acid in order to dis-charge again the mordants previously applied in some parts of the cloth, itwill be seen that after the cleansing, washing, madder dyeing, and clearingoperations the discharge material, acid in this case, has readily corroded thealuminous mordant, and also readily enough the tin mordant wherever thesetwo were applied singly, but in all portions of the cloth where the twomordants are placed upon each other no such discharging aCtion has takenplace. On leaving the dye-beck the colours produced, wherever the twomordants come together, are as intense and deep as if no acid had ever been

* Among them M. H. Schlumberger, jun., M. Previnaire, M. Pincoffs, M. Salomonson,Professor Van der Boon Mesch, and others. These experiments were made at Haarlem, atEnschede, and partly also at Rotterdam and Ghent.