Permanent Colours of Opaki BoJies. 177 



ftandy obferved, thac whenever colourmg par- 

 ticles become opake, their fize renders them 

 incapable of entering the pores of wool, filk, 

 cotton, or linen, or of cohering to their furface. 

 For, the attraftive force, by which particles tend 

 mutually to each other, and cohere, is weakened, 

 in proportion as their bulk increafes, fo that the 

 degree of magnitude of the colouring particles, 

 which is effential to the opacity of liquors, is 

 inconfiftent with the minutenefs, requifite to 

 thole means of union, by which dying is effc6ted. 



I fhall felcfl one inftance, from amongft many 

 which are applicable to thefe obfervations. I 

 infufed, in a pint of diftilled water, fuch a quan- 

 tity of fuftic, that the water was faturated with 

 its colouring particles. The aqueous part of 

 this infufion was evaporated by a gentle, but 

 continued, heat, till it was reduced to a folid 

 mafs. 



The liquor, during every part of this procefs, 

 continued tranfparent, and the folid extra(5t, 

 which it yielded, tranfmitted a yellow colour, 

 when fpread thin, but appeared blacky when 

 thicker mafles were viewed. 



Having prepared another pint of the fame in- 

 fufion, I evaporated half of the water, and 'left 

 tlie remainder, till it was cold. In this flate it 

 became turbid, and opake. When this liquor 

 was filtered, a tranfparent infufion pafled through 

 the filter, and an opake fecula was retained by 



Vol. II. N the 



