chemical Properties attributed to Light. 457 
its metallic splendour, began to make their appearance here 
and there on the surface of the charcoal ; and, in six hours, the 
solution, which at first was of a bright yellow colour, became 
. perfectly colourless, and as clear and transparent as the 
PUREST WATER. 
The surface of the charcoal was, in several places, nearly 
covered with small particles of revived gold ; and the inside 
of the glass tube, in that part where it w'as in contact with the 
upper surface of the contained liquid, was most beautifully 
gilded. 
This gilding of the tube was very splendid, when viewed by 
reflected light ; but, when the tube was placed between the 
light and the eye, it appeared like a thin cloud, of a greenish 
blue colour, without the smallest appearance of any metallic 
splendour. 
From the colour, and apparent density of this cloud, I was 
induced to conclude, that the gilding on the glass was less than 
one millionth part of an inch in thickness. 
This interesting experiment was repeated six times, and al- 
ways with nearly the same result. The gold was completely 
revived in each of them, and the solution left perfectly colour- 
less ; in most of the experiments, however, the sides of the 
glass were not gilded, all the revived gold remaining attached 
to the surface of the charcoal. 
In two of these experiments, I made use of pieces of charcoal 
which had been previously boiled several hours in a large quan- 
tity of distilled water, and which were introduced wet , and hot , 
into the tube, and immediately covered by the solution, to 
prevent them from imbibing any air ; and, in different experi- 
ments, the solution was used of different degrees of strength, 
MDCCXCVI1I. 3 N 
