Chemical Properties attributed to Light. 85 



been, after seeing the results of these experiments, to 

 find out whether gold could be revived from this aque- 

 ous solution of its oxide by means of charcoal, without 

 the assistance of light, and merely by such a degree of 

 equal heat as could be given to it in the dark. To 

 determine that important question, the following ex- 

 periment was made : — 



Experiment No. 10. — A cylindrical glass tube, -fo of 

 an inch in diameter and 10 inches long, closed her- 

 metically at its lower end, and containing a quantity 

 of a diluted aqueous solution of' the oxide of gold 

 mixed with charcoal in broken pieces, about the size of 

 large peas, was put into a fit cylindrical tin case, which 

 was nicely closed with a fit cover ; and the glass tube, 

 with its contents so shut up in the dark, was exposed 

 two hours in the temperature of 210° of Fahrenheit's 

 scale. 



On taking the glass tube out of its tin case, I found 

 the solution perfectly colourless, and the revived gold 

 adhering to the surface of the charcoal. 



On repeating the experiment, and using the solution 

 nearly saturated with the oxide, the result was precisely 

 the same ; the solution being found perfectly colour- 

 less, and the revived gold adhering to the surface of 

 the charcoal. 



I own fairly that the results of these last experi- 

 ments were quite contrary to my expectations, and 

 that I am not able to reconcile them with my hypothe- 

 sis respecting the causes of the reduction of the oxide, 

 in the foregoing experiments; but, whatever may be 

 the fate of this or of any other hypothesis of mine, I 

 hope and trust that I never shall be so weak as to feel 

 pain at the discovery of truth, however contrary it may 



