1857.] of Gold (and other Metals) to Light. 431 



of division, were retained in that state for the time by their 

 adhesion to the glass. Of course chemical change was free to 

 occur, but not a change dependent upon their mutual aggrega- 

 tion ; yet they were not held by any special chemical attraction 

 to, or combination with, the glass ; for a touch with a card, a 

 feather, or the finger, was sufficient to remove them at once ; 

 and if rubbed off with a point of wood, they coated it with bril- 

 liant metallic gold. 



Again, though these particles are so finely divided that they 

 pass easily through ordinary filters, still a close filter catches 

 some ; and if a ruby fluid be passed through again and again, 

 the paper at last becomes of a rosy hue, because of the gold 

 which adheres to it; being then well-washed, and, if needful, 

 dried, the gold is again ready for experiment. Such gold 

 paper, placed across the middle of the dark tube and examined 

 by transmitted light, was of the same ruby tint as when looked 

 through in the open air. It was unaffected by salt or brine, 

 though these, added to the rosy fluid which had passed the 

 filter, instantly changed it to violet-blue. Portions of the paper 

 were put into separate glasses with brine, solutions of hydro- 

 chloric, nitric and sulphuric acids, ammonia, potassa, soda and 

 sulphuretted hydrogen, but no change occurred with any of 

 them in two days. On the other hand, a very dilute solution 

 of chlorine immediately turned the ruby to blue, and then 

 gradually dissolved the gold. A piece of the ruby paper im- 

 mersed in a strong solution of cyanide of potassium suffered a 

 very slow action, if any, and remained unaltered in colour ; 

 being brought out into the air, the gold very gradually dis- 

 solved, becoming first blue. A portion of the ruby paper was 

 dried and heated in oil until the oil and the paper began to 

 change their hue ; the gold had not altered in its colour or 

 character. Another portion was heated in the vapour of 

 alcohol and also of ether until the paper began to alter ; 

 the gold remained unaltered. A blue fluid being passed 

 oftentimes through a filter gave a blue paper, which, being 

 washed and tried in the same manner, was found to contain 

 particles unchanged by the simple acids or alkalies, or by 

 heat or vapours, but dissolving, as gold would do, in chlorine 

 or nitromuriatic acid. These tests are, I think, sufficient to 

 prove the metallic nature and permanence of the gold as it 



