CHEMISTRY. 273 



attached to the glass: it ma}- be experimented with, though in a state of 

 extreme tenacit}-. Examined either by the electric lamp, or the solar spec- 

 trum, or the microscope, this film was apparently continuous in mairy parts 

 where its thickness could not be a tenth or twentieth part of the original gold 

 leaf. In these parts gold appeared as a very transparent thing, reflecting yel- 

 low light, and transmitting green and other rays ; it was so thin that it pro- 

 bably did not occupy more than a hundredth part of a vibration of light, and 

 yet there was no peculiar effect produced. The rays of the spectrum were 

 in succession sent through it ; a part of all of them was either stopped or 

 turned back, but that which passed through was unchanged in its character, 

 whether the gold plate was under ordinary circumstances, or in a very intense * 

 magnetic field of force. When a solution of gold is placed in an atmosphere 

 containing phosphorus vapor the gold is reduced, forming films that may be 

 washed and placed on glass, without destroying their state or condition; 

 these vary from extreme thinness to the thickness of gold leaf or more, and 

 have various degrees of reflective and transmissive power; they are of great 

 variety of color, from grey to green, but they are like the gold leaves in 

 that they do not change the rays of light. When gold wires are deflagrated 

 by the Leyden discharge upon glass plates, extreme division into particles is 

 effected, and deposits are produced, appearing by transmitted light of many 

 varieties of color, amongst which are ruby, violet, purple, green, and grey 

 tints. By heat many of these are changed so as to transmit chiefly ruby 

 tints, relieving always the reflective character of gold. None of them affect 

 any particular ray selected from the solar spectrum, so as to change its cha- 

 racter, other than by reflection and absorption; what is transmitted still 

 remains the same ray. When gold leaf is heated on glass, the heat causes its 

 retraction or running together. To comjnon observation the gold leaf disap- 

 pears, and but little light is then reflected and stopped ; but if pressure by a 

 polished agate convex surface be applied to the gold in such places, reflective 

 power reappears to a greater or smaller degree, and green light is again trans- 

 mitted. TVhen the gold films by phosphorus have been properly heated, pres- 

 sure has the same effect upon them. If a piece of clean phosphorus be 

 placed beneath a weak gold solution, and especially if the phosphorus be 

 a clear thick film, obtained by the evaporation of a solution of that sub- 

 stance in sulphide of carbon, in the course of a few hours the solution be- 

 comes colored of a ruby tint ; and the effect goes on increasing, sometimes 

 for 2 or 3 days. At times the liquid appears clear, at others turbid. As 

 far as Mr. Faraday has proceeded, he believes this fluid to be a mixture of 

 a colorless transparent liquid, with fine particles of gold. By transmitted 

 light it is of a fine ruby tint ; by reflected light it has more or less of a brown- 

 yellow color. That it is merely a diffusion of fine particles is shown by two 

 results the first is, that the fluid being left long enough, the particles settle 

 to the bottom ; the second is, that whilst it is colored or turbid, if a cone of 

 the sun's rays (or that from a lamp or candle in a dark room) be thrown 

 across the fluid by a lens, the particles are illuminated, reflect yellow light, 

 and become visible, not as independent particles, but as a cloud. Sometimes 

 a liquid which has deposited much of its gold, remains of a faint ruby tint, 



12* 



