454 0" '^^ Chemical Properties attribuUd to Liglt. 



of the ioTivs under which gold and filver are revived from their oxides, in this procefs, be 

 owing to the difference of the fpecific gravities of thofe metals ? 



The following experiments, which were firft fuggefled by an accident, were made with 

 a view to inveftigate ftill farther the caufes of thofe efFeds which have been attributed to 

 the fuppofed chemical properties of light. 



Having accidentally put away two fmall phials, each containing a quantity of aqueous 

 folution of the oxide of gold and fulphuric ether, in each of which the ether had extradled 

 the gold completely from the folution, as was evident by the yellow colour of the folution 

 having been transferred to the ether, and the folution being left colourlefs ; in one of the 

 phials, which happened to ftand in a window in which there was occafionally a flrong 

 light (though the direft rays of the fun never fell on it), I found, in about three weeks, that 

 the oxide was almoft entirely reduced ; the revived gold appearing in all its metallic fpien- 

 dour in the form of a thin pellicle, fwimming on the furface of the aqueous liquor in the 

 phial, and the colour of the ether which repofed on it having become quite faint; while no 

 vifiblc change had been produced in the contents of the other phial, which had flood in a 

 dark corner of the room. 



As thefe appearances induced me to fufpcdl:, or rather (trengthencd the fnfpicions I had 

 before conceived, that the reparation of gold from ether, under its metallic form, when a. 

 folution of its oxide is mixed with that fluid, is always effeded by a redudion of the oxide 

 by means of light, I made the following experiment, with a view to the farther inveftiga-- 

 tion of that matter. 



Experiment No. 1 3. Into a fmall pear-like phial of very fine tranfparent glafs I put equal 

 quantities of an aqueous folution of the muriatic oxide of gold and fulphuric ether; and 

 the phial, which was about h;.lf filled, being clofcd with a good cork well fecured in its place, 

 was expofed to the adion of the direft rays of a bright fun. 



A pellicle of revived gold, in all its metallic fplendour, began almoft immediately to be 

 formed on the furface of the aqueous liquid, and foon covered it entirely ; and at the end' 

 of two hours the whole of the oxide was completely reduced, as was evident from the ap- 

 pearance of the ether, which became perfeff/y colourlefs. 



On (baking the phial, the metallic pellicle, which covered the furface of the aqueous Ii^ 

 quid, was broken into fmall pieces, which had exafUy the appearance of leaf-gold, pofTelT- 

 ing the true colour and all the metallic brilliancy of that metal. 



On fufFering the phial to ftand quiet, the aqueous liquor and the ether feparated, and 

 moft of the broken pieces of the thin Iheet of gold defcended to the bottom of the phial : 

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

 as the aqueous liquid, appeared to be perfe£tly tranfparent znA colourlefs. 



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

 rate, I thought I could perceive that the ether had loft fomething of its fluidity ; but aa 

 this was an event I expected, it is the more likely, on that account, that 1 was deceived, 

 when I imagined I faw proofs of its having taken place. 



On removing the cork, after the contents of the bottle had been fufFered to cool, there 

 was no appearance of any confiderable quantity of air, or other permanently elaftic fluid, 

 having been either generated or abforbed during the experiment. 



Finding that the oxide of gold might be fo completely and fo expeditloufly reduced by 



means 



