MORDANTS.

303

general rule it should be observed that the mordants ought to be saturated,and since the shade desired is dependent upon the strength of the mordantsapplied, it is evident that this condition will influence the quantity of madderrequired. When the mordants are used too strong and their full saturationnot obtained (that is to say, plenty of dye-stuff present in excess), there is agreat risk of inequalities arising in the results. The best way to fulfil all re-quirements is to have sample patterns printed in stripes with the identicalmordants applied to the goods attached to them when immersed in the dye-beck, and therefore simultaneously dyed, and to use the results as a guide tothe proper quantity of dye-stuff.

According to M. H. Schlumberger’s researches, mordants may within certainlimits be supersaturated by an excess of madder without impairing therebythe brightness of the shades, provided care be taken to adjust the quantityof the water in the dye-beck in due proportion to the madder. If this is notproperly regulated after clearing the shades obtained are spotted, unequal, anddull. Contadl of air does not interfere. The materials of which the dye-becks are constructed exercise a great influence on the results when theheating is effected by means of open fire or by a water-bath, but with theapplication of steam the material becomes of no importance whatever. Whenmetal-made dye-becks are used heated by open fire or a water-bath it veryfrequently happens that a loss of some 40 per cent of dye material is ex-perienced, but this decrease is not observed when steam is used, and is, more-over, only observed with madder, not with garancin or any other of its com-mercial derivatives, and the loss is therefore due to the unequal influenceexercised by the soluble particles of the madder. As a general rule it may besaid that the addition of various substances to the dye-beck along with themadder in order to increase its tinctorial power, and to attract a larger pro-portion of its aCtive principles, has never yielded favourable results.

In the paper published by M. H. Schlumberger,* and reproduced by M. J.Persoz in his celebrated work “TraitC de L’impression,”f will be found a longlist of substances drawn up by a German chemist, with the view of showingthe value of a large number of substances used as additions to the madder-bath. It is needless to enter into further'details on this subject, since ex-perience has proved the uselessness of such additions, none of which, more-over, have any scientific interest.

We must not, however, negleCt to notice the favourable effect of a certainquantity of oxalate of ammonia as an addition to the dye-beck when madderis employed, as first observed by M. E. Schwartz. The addition of this saltgives rise, in all probability, to a double decomposition ensuing between it andthe lime salts of an organic as well as of organic acids contained in themadder. The colouring matter combined with these salts is thus set free,while the oxalic acid seizes upon the lime.J The addition of alkalies or chalkma y or may not be useful according to the proportion thereof employed, andthe nature of the madder worked with. Since Alsace and Zealand madderare both acid, the former, however, far more so than the latter, and contain

* “ Bulletin de la Societe Industrielle de Mulhouse,” vol. viii., pp. 293 to 360.

+ Persoz, “ Traite de L’impression des Tissus,” vol. ii., p. 503 and following.

t We need scarcely remark that to add oxalate of ammonia along with chalk is a mere wasteof materials. Where either of thes^substances is beneficial the other is likely to be injurious.