96 An Inquiry concerning the 



introduced it into a small phial with a wide mouth, 

 nearly filled with a diluted solution of nitrate of silver, 

 where it was suffered to remain in a dark closet till the 

 ivory had acquired a bright yellow colour. The slip 

 of ivory was then taken out of the phial, and immersed 

 in a tumbler of pure water, and immediately exposed 

 in the water to the direct rays of a bright sun. 



The instant the sunbeams fell upon the ivory it 

 began to change colour, and in less than two minutes 

 from being of a very beautiful yellow it became quite 

 black. 



The rapidity with which this change of colour takes 

 place is very striking, and renders the experiment 

 uncommonly interesting. On examining the ivory, 

 its surface was found to be covered with a fine coaly 

 substance, which was easily rubbed off with the hand. 



On removing this coaly substance, after the ivory 

 had been suffered to remain two or three hours ex- 

 posed in water to the action of the sun's light, the sur- 

 face of the ivory was found to be completely silvered 

 over, so as perfectly to resemble a slip of metal. 



Although this coating of revived metal which covers 

 the surface of the ivory is very thin, yet, if the ivory be 

 well soaked in the solution of nitrate of silver, the oxide 

 of that metal will penetrate the ivory to a considerable 

 depth ; and as fast as the silvering wears off from the 

 surface of the ivory, the oxide below it being uncovered 

 and exposed to the light, a new coating of revived 

 metal will be formed to replace it, and the surface of 

 the ivory will not lose its metallic appearance. 



I tried by a similar process to gild a slip of ivory 

 with gold, but in this attempt I did not succeed as well 

 as I could have wished. A slip of ivory which had 



