Ji82 ]\femoir upon the Mordants 



fectual to find a substitute for alum, we have, nevertheless, 

 made trial of a great nauiber of substances uith wool, 

 less, however, for the purpose of discovering the best niorr 

 dants, ihan for determining the action of several substances, 

 very soluble, and at the same time endowed with srreat 

 powers. We boiled wool for two hours in water, in which 

 were put small quantities of sulphuric, nitric, muriatic, 

 and tartaric acids. In each instance, the wool, especially 

 when Combined with sulphuric acid, struck with cochineal 

 and madder deeper colours than when impregnated with 

 alum and tartar. No doubt, therefore, can be entertained 

 of their buperiority in similar c^ses ; but of all the mor- 

 dants wc tried, there is not one which gives such bright 

 colours as what are obtained by means of the acid tartrite 

 of alumina (notwiihslanding the opinion of M. Hausmann 

 to the contrary). This salt would, in a great number of 

 cases, be preferable to tartar and alum, if its price was not 

 so much higher than theirs. Whilst we were occupied in 

 niquiring with the greatest cafe into everv thing relative to 

 the nature and mode of combination of mordants with 

 various stufls, we did not forget to examine the several 

 inethods which have been adopted in all I he workshops for 

 a long time past, in order to ascertain if the proportions of 

 alum and tartar, the mtost generally employed, were those 

 the most suitable for the purpose, if the time employed for 

 the alum bath was sufficient to impregnate the wool suffi- 

 ciently, and if the exposure to the cool air afterwards, for 

 severa! days, which js so generally thought necessary, is at- 

 tended with the expected advantages. 



Equal parts of the mordants, that is, half the weight of 

 the stuff, produced no better effect than one-fourth ; but 

 between this quantity and one-twentieth part, the colours 

 of cochineal, kermes, an4 niadder, were weaker in pro- 

 portion to the diminution of the quantity of the salts ; 

 whilst, on the contrary, the effects were reversed with 

 wqad Slid Brazil wood, so that in these last substances, the 

 colour was deeper tlie more the salts were diminished. No 

 difference could be observed in the colour whether the wools 

 had been in ttie alum bath for two, four, or six hours ; it 

 ]s, therefore, useless to continue stuffs in the bath longer 

 than tw<> hours. Our experiments did not discover that 

 there was any difference in the colour, whether the dyeing 

 took place immediately after the aluminir, or was protracted 

 for SQine time, except only that wool impregnated with 

 alum alone, produced a deeper colour with woad, after 

 having been exposed some time to a cool air^ \yhich vve 



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