ai ObjeSls of the Art of Dyings i^c. 395 



being difficult of folution in water, detaining 

 the colouring particles, which are farther ce- 

 mented by the crude tartar. 



But though thefe fairs are not eafily foluble in 

 water, yet a fufficient quantity of water will 

 diflblve them; and, if the colouring particles 

 were attached to them, they mud be carried off 

 whenever the folution of the faks is effeded. 

 But as this is not the cafe (for when thefe par- 

 ticles are properly affixed to the material, they 

 are not moveable by any quantity of water, how- 

 ever large) their fixity muft depend on fome 

 more permanent bails. 



Mr. Keir, the ingenious tranflator of Mac- 

 quer's Diflionary of Chemiftry, appears to have 

 been the firft who fufpefted that the earth of alum 

 was precipitated, and in this form attached to 

 the material. Indeed it feems wonderful that this 

 idea did not occur to M. Hellot, who was fully 

 aware that in the dying of fcarlet, the cochineal 

 became firmly united to the white calx of tin, 



M. Macquer, in the laft edition of his Dic- 

 tionary, has been more explicit on this fubjedt. 

 From the experiments which have been alluded to, 

 in the fecond part of this paper, by which laques 

 and carmine are made by pouring folutions of 

 alum or of tin, into clear decoclions of extrac- 

 tive refinous colouring ingredients, he concludes 

 that the fame efi^efls take place in dying ; 

 that when the materials are loaded with thefe 



earthy 



