218 ANNUAL OF SCIENTIFIC DISCOVERY. 



the investigations then announced was published in the Annual of Scientific 

 Discovery for 1857, pp. 272, 273, 274. Since, another communication has 

 been made by Prof. Faraday, on the same subject, in which he states that 

 having since obtained some perfectly pure gold leaf, he has been enabled to 

 fully verify his former observations. This was the more important in re- 

 gard to the effect of heat in taking away the green color of the transmitted 

 light, and destroying, to a large extent, the power of reflexion. The tem- 

 perature of boiling oil, if continued long enough, is sufficient for this effect ; 

 but a higher temperature (far short of fusion) produces it more rapidly. 

 Whether it is the result of a mere breaking up by refraction of a corrugated 

 film, or an allotropic change, is uncertain. Pressure restores the green color ; 

 but it also has the like effect upon films obtained by other processes than 

 beating. Corresponding results are produced with other metals. As before 

 stated, films of gold may be obtained on a weak solution of the metal, by 

 bringing an atmosphere containing vapors of phosphorus into contact with 

 it. They are produced, also, when small particles of phosphorus are placed 

 floating on such a solution; and then, as a film differing in thickness is 

 formed, the concentric rings due to Newton's thin plates are produced. 

 These films transmit light of various colors. When heated they become 

 amethystine or ruby; and then when pressed, become green, just as hc:i!cd 

 gold leaf. This effect of pressure is characteristic of metallic gold, whether 

 it is in leaf, or film, or dust. Gold wire, separated into very fine particles 

 by the electric deflaymlion, produces a deposit on glass, which, being exam- 

 ined, either chemically or physically, proves to be pure metallic gold. This 

 deposit transmits various colored rays : some parts arc gray, others green, 

 or amethystine, or even a bright ruby. In order to remove any possibility 

 of a compound of gold, as an oxide, being present, the deflagrations were 

 made upon topaz, mica, and rock crystal, as well as glass, and also in atmos- 

 pheres of carbonic acid and of hydrogen. Still, the results were the same, 

 and ruby gold appeared in one case as much as in another. Being heated, 

 all parts of the deposit became of an amethystine or ruby color ; and by 

 pressure, these parts could be changed so as to transmit the green ray. The 

 production of fluids, consisting of very finely divided particles of gold dif- 

 fused through water, was spoken of before. These fluids may be of vari- 

 ous colors by transmitted light from ruby to blue ; the effects being produced 

 only by diffused particles of metallic gold. If a drop of solution of phos- 

 phorus in bisulphide of carbon be put into a bottle containing a quart or 

 more of very weak solution of gold, and the whole be agitated, the change 

 is brought about sooner than by the process formerly described ; or if a so- 

 lution of phosphorus in ether be employed, very quickly indeed ; so that a 

 few hours' standing completes the action. All the preparations have tho 

 same qualities as those before described. The differently colored fluids may 

 have the colored particles partially removed by filtration ; and so long as 

 the particles are kept by the filter from aggregation, they preserve their ruby 

 or other color unchanged, even though salt be present. If fine isinglass be 

 soaked in water, then warmed to melt it, and one of these rich fluids bo 

 added, with agitation, a ruby jelly fluid will be obtained, which, when sufii- 



