DIVISIBILITY OF GOLD AND OTHER METALS, yj 



and sending the part of the cone near the focus into the fluid ; the cone 

 becomes visible, and though the illuminated particles cannot be dis- 

 tinguished, because of their minuteness, yet the light they reflect 

 is golden in character and seen to be abundant in proportion to the 

 quantity of gold present. Portions of gold so dilute as to show no 

 trace of gold by color or appearance can have the presence of the 

 difliised solid particles rendered evident by the sun in tliis way. . . . 

 The state of division of these particles must be extreme; they have 

 not as yet been seen by any power of the microscope." 



Faraday further tells us that he endeavored to obtain an idea 

 of the quantity of gold in a given ruby fluid, and for this purpose 

 selected a plate of gold ruby glass, of good full color, to serve as a 

 standard, and he compared the different fluids with it, varying their 

 depth until the light from white paper, transmitted through them, 

 was apparently equal to that transmitted by the standard glass. 

 Then, known quantities of these ruby fluids were evaporated to dry- 

 ness, the gold converted into chloride, and compared, by reduction 

 on glass and otherwise, with solutions of gold of known strength. 

 "From these considerations it would appear that one volume of gold 

 is present in the ruby fluid in about "750,600 volumes of water; and 

 that, whatever the state of division to which the gold may be re- 

 duced, still the proportion of the solid particles to the amount of 

 space through which they are dispersed must be of this extreme pro- 

 portion. This accords perfectly with their invisibility in the micro- 

 scope ; with the manner of their separation from the dissolved state; 

 with the length of time during which they can remain diff'used ; and 

 with their appearance when illuminated by the cone of the sun's rays." 



While all the statements of this profound investigator were so 

 carefully kept within the limit of actual observation, he tells us, in 

 conclusion, that he not only believed the gold to be diffused in solid 

 metallic particles, but that he also believed " there may be particles 

 so fine as to reflect very little light indeed, that function being almost 

 gone." 



The art of gold-plating has become so extensive in its application 

 to a great variety of ornamental objects, that it seemed to the writer 

 an interesting question " How thick a film is required to produce a 

 fine gold-color? " He was unable to find, on inquiry, that any careful 

 notes to determine this point have been recorded,' and he recently 

 made some experiments with the following results : A sheet of copper 

 was rolled down to an average thickness of joVo ^^ ^^ inch. Two 

 plates were cut from this strip, 4 by 2^ inches, having a metallic sur- 

 face of twenty square inches each. These plates were boiled in 

 alkali, to remove grease, polished, and accurately weighed on a bal- 



' It is stated that when a cylindrical bar of silver is coated with gold and drawn into 

 the fine wire used in embroidered housings, etc., a grain of gold will cover 345.6 feet 

 of wire. 



