Permanent Colours of Opake Bo die si 24^ 



judged it expedient to examine in what manner 

 the particles of that metal, combined with glafs, 

 would, under various circumftances, adt upon 

 the differently refrangible rays. 



For this purpofe, 1 combined gold with pellu- 

 cid colourlefs glafs, after the manner of Kunckel, 

 CafTius, and others, by which a Tranfparent 

 Coloured Glafs v/as compofed, which tranfmitted 

 a bright red colour, but appeared black by inci- 

 dent light. 



I expofed feveral pieces of this red glafs to 

 the heat of burning coals •, by which means, 

 they loft their tranfparency, and underwent an 

 alteration in their texture. For, when the red 

 glafs is thus reheated, the particles of gold, uni- 

 tiog with fome of the other ingredients of the 

 glafs, form Opake Molecule:, which refled all 

 the rays, excepting the violet, and thereby 

 appear by incident light, of a light brown hue. 



\( all the rays were equally reflcfled, the mafs 

 would appear white, when viewed by incident 

 light. But, the privation, of even a fmall 

 portion of them, impairs the whitenefs, and 

 reduces it to a brown hue, which is lighter, or 

 more intenfe, as a greater or lefs quantity of 

 the different rays are wanting in its compofition. 



The brown hue, reflecfled from the glafs, 

 which is here inftanced, arifes from the white 

 light refleded from the Opake Particles, to 

 which a fmall proportion of all the rays, excepting 

 the violet, is fuperadded. 



K 2 The 



