Polytechnic Association Proceedings. 927 



physical and cheiucal properties of gold. 



Pure gold is of a reddish 3'ellow color, and possesses a high 

 metallic luster. In the pulverulent state it is brown and dull, but 

 acquires metallic luster by pressure. The specific gravity of 

 melted gold is 18.2, of hammered gold, from 18.3 to 19.4. Finely 

 divided gold precipitated by sulphate of iron was found to vary 

 in density from 19.55 to 19.72, and when precipitated by oxalic 

 acid, its density was 19.49. Its chemical equivalent of combina- 

 tion is 196.44, its formula Au., aurum; its alchemistic sign, ©, or 

 Sol, the sun, the emblem of purity. 



In a pure state, gold is softer than silver, and nearly as soft as 

 lead, but its tenacity is so great that it may be drawn out into very 

 fine wire. It is extremely malleable, and can be hammered out 

 into leaves only ^fi^'^'^ ^^ ^^ ^^^ ^ thickness. The same amount 

 of leaves (370,000) made of printing paper w^ould reach nearly a 

 hundred feet high. A single grain of gold may be extended over 

 57.75 square inches of surface, or di-awn out into a wire five hun- 

 dred feet long. Reamur, by rolling out a fine silver wire covered 

 with gold, reduced the coating of gold to the twelve-millionth of 

 an inch in thickness, and the surface appeared to be perfect when 

 viewed under the microscope. 



Gold does not directly combine with oxygen, and therefore 

 sufi(t?rs no change by exposure to air and moisture at any tempera- 

 ture, not even by being kept in a state of fusion in open vessels. 



I intend, so soon as I shall have sufficient time, to institute a 

 series of experiments for the purpose of ascertaining the influence 

 of the metalloids in vapor form on precipitated gold under different 

 degrees of heat, also how far electricity influences its chemical 

 character and stability. 



Gold, under ordinary circumstances, and in its metallic form, is 

 not attacked by the mineral, or any of the simple acids, except by 

 selenic acid, with the aid of heat. Iodine has only a weak action 

 upon it, but bromine and chlorine attack it easily at ordinary tem- 

 peratures, and it is dissolved by any substance that liberates chlorine. 

 It is therefore dissolved by hj'^drochloric acid, if binoxide of man- 

 ganese, chromic acid, etc., be added. The usual solvent is a 

 mixture of one part of nitric and four parts of hydrochloric acids. 

 The proper solvent for gold is nascent chlorine, which is eliminated 

 by the mutual action of the mixed acids. 



Gold is one of the most perfect conductors, both of heat and 

 of electricity. It fuses at bright red heat, the temperature of which 



