as ObjeSfs of the Art of Dying, &c. ^^^ 



pofition : and the colouring principle, having a 

 ftrong attraftion to the earth, and this to the 

 fubftance to be dyed, a reparation from the 

 water is eafily effefled, and the colour is capable 

 of being applied, and of adhering, in a durable 

 manner, without the intervention of any medium* 

 Of this tribe are galls, walnut rinds, and the 

 root of the tree, fumach, and alder barkj and 

 thefe are called root colours, as being the foun- 

 dation of others. 



2dly. Other articles of the materia tinEloria 

 confift of fuch materials, whofe parts are either 

 wholly extradive, or, though containing fome 

 refinous matter, are capable of being diflblved 

 in water alone; and being deficient in the earthy 

 principle, contained in the articles of the former 

 divifion, require that an earth be previo'ufly in- 

 troduced into the pores or interftices of the fub- 

 ftance, intended to be dyed ; to form a bafis, to 

 which the colour may adhere. Without this 

 medium the attradion of that fubftance to the 

 colouring matter would be fo weak as either 

 not to be able to feparate it from the water j or 

 if feparated, to retain and prevent it beino- re- 

 diflblved by the water, when aided by mecha- 

 nical means, or the addition of certain fubftances 

 which increafe its folvent powers, even in a 



fmall degree*. 



3dly. 



• Many of thefe colouring bodies, as well as thofe of 

 the firft divifion, alfo contain a principle, knowa by the 



appellation 



