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XXVI. Memoir upon the Mordants employ ed in the Jrt of 

 Dyeing. By MM. Thenard and Hoard. Read at 

 the Physical and Mathematical Class of the French In- 

 stitzUe. 



J. HE name of Mordant is given, in the art of dyeing, to 

 those substances which serve to prorkice a more intimate 

 combination of colouring matters with the different stuffs, 

 and to augment the brightness and beauty of them. This , 

 property belongs to a grcai number of saline and metallic 

 substances : but those which possess it in the highest de- 

 gree, and which, for this reason, are exclusively made use 

 of by dyers, are alum, acetate of alumina, tartar, and the 

 solutions of tin. 



An examinaiion and analysis of the effects produced by 

 these mordants upon vegetaole and animal substances, will 

 form the subject of the memoir we have honour to submit 

 (o the Class. We shall divide it into four chapters, where- 

 in we shall successively treat of the action of alum, of ace- 

 tate of alumina, of alum and tartar, and of the solutions of 

 tin, upon silk, v.ool, cotton, and thread, according to the 

 juethods most generally made use of in the art of dyeing. 



CHAP. J.—OfJlum, 



The manner of applying the alum varies according to 

 the nature of the stuiTs, and according to the colours we 

 w ibh to obtain. Siiks are permitted to macerate for several 

 davs in a solution of alum, sufficiently diluted for the salt 

 not to crystallize. VV^ool is boiled for two hours in wa- 

 ter, containing a fourth part of its weight of alum. Cotton 

 and thread are soaked for at least twenty -four hours in 

 warm concentrated solutions or alum, to which frequently 

 some potass is addtd. It has hitherto been thought that 

 in this operation the alun) is decomposed, and that the alu- 

 mina combines with the stufl', causing it thereby the more 

 easily to take the colour when plunged into the dyeing 

 bath ; but the experiments we have made induce us to adopt 

 a different opinion. 



Art. 1 . — Analysis of the almning of Silk. 



Ninety-five trrammes of siik, well cleaned and perfectly 

 purified, were 'infused in a glass vessel during six days, at 

 the con)mon temperature of the atmosphere, with four 

 quarts of distilled water, containing 100 gnuumes of pure 

 alum, which had been previously dissolved in it. After 



standing 



