1856.] on Divided Gold, 31 1 



the gold plate was under ordinary circumstances, or in a very in- 

 tense magnetic field of force. 



When a solution of gold is placed in an atmosphere containing 

 phosphorus vapour the gold is reduced, forming films that may be 

 washed and placed on glass without destroying their state or condi- 

 tion : 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 colour, 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 

 colour, amongst which are ruby, violet, purple, green, and grey 

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

 ruby tints, retaining always the reflective character of gold. None 

 of them aflTect any particular ray selected from the solar spectrum, 

 so as to change its character, otherwise 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 and run- 

 ning together. To common observation the gold leaf disappears, 

 and but little light is then reflected or 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 transmitted. When the gold films by phos- 

 phorus have been properly heated, pressure has the same eflect 

 with 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 substance in sul- 

 phide of carbon, in the course of a few hours the solution becomes 

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

 for two or three days. At times the liquid appears clear, at other 

 times turbid. As far as Mr. Faraday has proceeded, he believes this 

 fluid to be a mixture of a colourless transparent liquid, with fine par- 

 ticles of gold. By transmitted light, it is of a fine ruby tint ; by reflect- 

 ed light, it has more or less of a brown yellow colour. That it is 

 merely a diff*usion 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 coloured 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, and to the ordinary observation, 

 transparent ; but when illuminated by a cone of rays the suspended 

 particles show their presence by the opalescence, which is the result 

 of their united action. The settling particles, if in a flask, appear 



Vol. II. Y 



