employed in the Art of Dyeing. 1 8 1 



rigorously demonstrated, we repeated this experiment, al- 

 though a very tedious one, in the method already pointed 

 out in the preceding chapters. 



Art. 2. — Of the Action of Alum and Tartar upon Wool. 



Before treating the wool with alum and cream of tartar, 

 we made some trials of the reciprocal action of tiicse two 

 salts. We ascertained that water, at the temperature of 

 12" or 14^, (53 F.) holds in solution only -^ part of its 

 weight of cream of tartar, that boiling water dissolves J- 

 of its N^eight, and that a mixture of equal parts of alum 

 and cream of tartar, dissolves in 3- the quantity of water 

 required to dissolve the salts separately at the same tem- 

 perature. These results do not difler from those already 

 obtained by M. Bertholtet, who has shown that alum has 

 the property of increasing the solubility of cream of tartar. 



If wool is alumed in the ordinary proportions, which 

 are i of the weight of the stuff of alum, and yU of cream 

 of tartar, all the substances being perfectly pure, we ob- 

 tain from the bath when evaporated, alum, cream of tartar, 

 and a residue difBculllv cr\r>laUizable, composed of tar- 

 trite of potass and an animal matter; the washings of the 

 woo! will give alum, a small quantity, scarcely apprcliable, 

 of cream of tartar, and a verv acid combination, formed of 

 a large quantity of tartaruus acid, alum, and animal matter. 



These experiments remove ail uncertainty concerning 

 many practical facts, which at present are only noticed by 

 the dver in a vague way, and point out to hini the precise 

 method of api)lying the mordants according to the nature 

 of the colour he wishes to obtain. Indeed, since by mak- 

 inc use of alum and tartar, the wool is impregnated with 

 aliun and a large quantity of tartarous acid, these two salts 

 should never be employed together, except when the co- 

 lour is suscei)tit)le of being- heiiihtened and rendered 

 brighter by acids, as is the case with cochineal, madder, 

 and kermes. On the contrary, ahun should never be em- 

 plovcd for wools intended to be dyed with woad or Brasil 

 wood, the colour of which is easily altered or destroyed by 

 acid->. Among all the vegetable and animal substances, we 

 have made choice of wool onlv for trial with alum and alum 

 and tartar, because it is onlv with this substance these mor- 

 dants are made use of in dyeing. 



Akt. 3. — On the Action of Acids, and of some Salts evi' 

 ployed us Mordants upon IFool. 



Although all researches hitherto made have been inef- 

 M 3 fcciual 



