VOL. LXXXVIII.] PHILOSOPHICAL TRANSACTIONS. 381 



Exper. 1 . Having evaporated to dryness a solution of fine gold in aqua regia, I 

 dissolved the residuum, in just as much distilled water as was necessary in order that 

 the solution, which was of a beautiful yellow colour, might not be disposed to 

 crystallize ; and, wetting the middle of a piece of white taffeta ribband, 1-l inch 

 wide, and about 8 inches long, in this solution, I held the ribband, with both my 

 hands, stretched horizontally over the clear bright flame of a wax candle; the under 

 side of the ribband being kept at the distance of about 14- inch above the point of the 

 flame. The result of this experiment was very striking. That part of the ribband 

 which was directly over the point of the flame, began almost immediately to emit 

 steam in dense clouds ; and in about 10 seconds a circular spot, about -£- of an inch 

 in diameter, having become nearly dry, a spot of a very fine purple colour, approach- 

 ing to crimson, suddenly made its appearance in the middle of it, and, spreading 

 rapidly on all sides, became, in 1 or 2 seconds more, nearly an inch in diameter. 

 By moving the ribband, so as to bring, in their turns, all the parts of it which had 

 been wetted with the solution to be exposed to the action of the current of hot 

 vapour that arose from the burning candle, all those parts which had been so wetted, 

 were tinged with the same beautiful purple colour. 



This colour, which was uncommonly brilliant, passed quite through the ribband, 

 and I found the stain to be perfectly indelible. I endeavoured to wash it out ; but no- 

 thing I applied to it, and among other things I tried super-oxygenated marine acid, 

 appeared in the smallest degree to diminish its lustre. The hue was not uniform, 

 but varied from a light crimson to a very deep purple, approaching to a reddish 

 brown. I searched, but in vain, for traces of revived gold, in its reguline form and 

 colour; but though I could not perceive that the ribband was gilded, it had all the 

 appearance of being covered with a thin coating of the most beautiful purple 

 enamel, which, in the sun, had a degree of brilliancy that was sometimes quite 

 dazzling. 



Exper. 2. A piece of the ribband which had been wetted with the aqueous solu- 

 tion of the oxide, was carefully dried in a dark closet, and was then exposed dry, 

 over the flame of a burning wax candle. The part of the ribband which had been 

 wetted with the solution, and which on drying had acquired a faint yellow colour, 

 was tinged of the same bright purple colour as was produced in the last- mentioned - 

 experiment, when the ribband was exposed wet to the action of the heat.* 



Exper. 3. A piece of the ribband which had been wetted with the solution, and 

 dried in the dark, was now wetted with distilled water, and exposed wet to the 

 action of the ascending current of hot vapour which arose from the burning can- 

 dle: the purple stain was produced as before, which extended as far as the ribband 

 had been wetted with the solution, but no farther. I afterwards varied this experi- 



* We shall hereafter find reason to conclude, that the success of this experiment, or the appearance 

 of the purple tinge, was owing to the watery vapour which existed in the hot current that ascended from 

 the flame of the candle. — Orig. 



3 c 2 



