VOL. LXXXVIII.] PHILOSOPHICAL TRANSACTIONS. 385 



The following experiments, which were first suggested by an accident, were 

 made with a view to investigate still further the causes of those effects which have 

 been attributed to the supposed chemical properties of light. Having accidentally 

 put away 2 small phials, each containing a quantity of aqueous solution of the 

 oxide of gold and sulphuric ether, in each of which the ether had extracted the 

 gold completely from the solution, as was evident by the yellow colour of the solu- 

 tion having been transferred to the ether, and the solution being left colourless ; 

 in one of the phials, which happened to stand in a window in which there was 

 occasionally a strong light, though the direct rays of the sun never fell on it, I 

 found, in about 3 weeks, that the oxide was almost entirely reduced ; the revived 

 gold appearing in all its metallic splendour, in the form of a thin pellicle, swimming 

 on the surface of the aqueous liquor in the phial, and the colour of the ether which 

 reposed on it having become quite faint ; while no visible change had been pro- 

 duced in the contents of the other phial, which had stood in a dark corner of the 

 room. As these appearances induced me to suspect, or rather strengthened the 

 suspicions I had before conceived, that the separation of gold from ether, under its 

 metallic form, when a solution of its oxide is mixed with that fluid, is always effected 

 by a reduction of the oxide by means of light, I made the following experiment, 

 with a view to the further investigation of that matter. 



Exper. 13. Into a small pear-like phial, of very fine transparent glass, I put 

 equal quantities of an aqueous solution of the muriatic oxide of gold and sulphuric 

 ether ; and the phial, which was about half filled, being closed with a good cork, 

 well secured in its place, was exposed to the action of the direct rays of a bright sun. 

 A pellicle of revived gold, in all its metallic splendour, began almost immediately to 

 be formed on the surface of the aqueous liquid, and soon covered it entirely ; and at 

 the end of 1 hours the whole of the oxide was completely reduced, as was evident 

 from the appearance of the ether, which became perfectly colourless. On shaking 

 the phial the metallic pellicle, which covered the surface of the aqueous liquid, was 

 broken into small pieces, which had exactly the appearance of leaf gold, possessing 

 the true colour, and all the metallic brilliancy, of that metal. On suffering the 

 phial to stand quiet, the aqueous liquor and the ether separated, and most of the 

 broken pieces of the thin sheet of gold descended to the bottom of the phial : the 

 remainder of them floated on the surface of the aqueous liquid ; and the ether, as 

 well as the aqueous liquid, appeared to be perfectly transparent and colourless. By 

 the length of time which was required for the ether and the aqueous liquid to se- 

 parate, I thought I could perceive that the ether had lost something of its fluidity ; 

 but as this was an event I expected, it is the more likely, on that account, that I was 

 deceived, when I imagined I saw proofs of its having taken place. On removing the 

 cork, after the contents of the bottle had been suffered to cool, there was no ap- 

 pearance of any considerable quantity of air, or other permanently elastic fluid, 

 having been either generated or absorbed, during the experiment. Finding that 

 the .oxide of gold might be so completely and so expeditiously reduced, by means 



vol. xvm. 3 D 



