Permanent Colours of Opake Bodies. 1 1 5 



" excefs of the intercepted rays tinging that 

 " whitenefs with their colour, when they are let 

 ** pafs." 



I have already (hewn, by numerous experi- 

 ments, in what manner coloured tinges are pro- 

 duced; and it uniformly appears, from all thole 

 experiments, that colours do not arife from re- 

 fleflion, but from tranfmitrion only. 



A folution of filver is pellucid and colourlefs. 

 A folution of gold (No. 18.) tranfmits yellow, 

 but refleds no colour. This metal alfo when 

 united with glafs, yields no colour by refleftion, 

 but by tranfmifTion only. 



All thefe circumftances feem to indicate, that 

 the yellow colour of gold arifes from a yellow 

 tranfparent matter, which is a conftituent part 

 of that metal, that it is equably mixed with 

 the white particles of the gold, and tranfmits 

 the light which is reflefled by them. In like 

 manner as when filver is gik, or foils are made 

 by covering white metals with Tranfparent Co- 

 lours. 



But, thefe fa6litious coverings are only fuper- 

 ficia), whereas ths yellow matter of gold is dif- 

 fufed throughout the whole fubfirance of the me- 

 tal, and appears to envelop and cover each of the 

 white particles. 



In whatfoever manner the yellow matter of 

 jgeld is united to its white fubftance, it exifts 

 in a rare Hate. For it bears only the fame 



JP 4 proportion 



