384 PHILOSOPHICAL TRANSACTIONS. [ANNO 1798. 



mentioned experiment had been boiled 1 hours in distilled water, by which means 

 its pores had been so completely filled with that fluid, that the pieces of it that 

 were used were specifically heavier than water, and sunk in it, to the bottom of the 

 containing vessel. Having been so successful in my attempts to reduce the oxide 

 of gold, by means of charcoal, in the moist way, I lost no time in making similar 

 experiments with the oxide of silver. 



Exper. 11. A solution of fine silver, in strong nitrous acid, was evaporated to 

 dryness, and the residuum re-dissolved in distilled water. A portion of this solu- 

 tion, which was perfectly colourless, diluted with twice as much distilled water, was 

 poured into a phial containing a number of small pieces of charcoal ; and the phial, 

 being well closed with a new cork stopple, was exposed to the action of the sun's 

 rays. In less than an hour, small specks of revived silver began to make their 

 appearance on the surface of the charcoal ; and at the end of 2 hours these specks 

 became very numerous, and had increased so much in size, that they were distinctly 

 visible to the naked eye, at the distance of more than 3 feet. They were very 

 white, and possessed the metallic splendour of silver in so high a degree, that when 

 enlightened by the sun's beams, their lustre was nearly equal to that of very small 

 diamonds. The phial, which was in the form of a pear, and about 1-|- inch in dia- 

 meter at its bulb, was very thin, and made of very fine colourless glass ; the aqueous 

 solution was also perfectly transparent and colourless ; and, when the contents of 

 the phial were illuminated by the direct rays of a bright sun, the contrast of the 

 white colour of these little metallic spangles with the black charcoal to which they 

 were fixed, and their extreme brilliancy, afforded a very beautiful and interesting 

 sight. As the air had been previously expelled from the charcoal, by boiling it in 

 distilled water, it was specifically heavier than the aqueous solution of the metallic 

 oxide, and consequently remained at the bottom of the bottle. 



Exper. 12. A phial, as nearly as possible like that used in the last experiment, 

 and containing the same quantity of diluted aqueous solution of nitrate of silver, 

 and also of charcoal, was inclosed in a cylindrical tin box, and exposed 1 hour to 

 the heat of boiling water, in an apparatus used for boiling potatoes in steam, for 

 the table. The result of this experiment was uncommonly striking. The surface 

 of the charcoal was covered with a most beautiful metallic vegetation ; small fila- 

 ments of revived silver, resembling fine flatted silver wire, pushing out from its 

 surface, in all directions ! Some of these metallic filaments were above one-tenth 

 of an inch in length. On agitating the contents of the phial, they were easily 

 detached from the surface of the charcoal, to which they seemed to adhere but 

 very slightly. These experiments were repeated several times, and always with 

 precisely the same results. When the oxide of gold was reduced in this way, the 

 revived metal appeared under the form of small scales, adhering firmly to the sur- 

 face of the charcoal. May not the difference of the forms under which gold and 

 silver are revived from their oxides, in this process, be owing to the difference of 

 the specific gravities of those metals ? 



