Formation of Gold Nuggets, 



55 



the bottom and sides of the vessel were gilded. Tartaric, 

 citric, and other organic acids have much the same effect. 

 With wood, bark, charcoal, and like substances, the reduction 

 is much slower. No carbonic acid is seen rising, and the 

 gold is deposited in the pores of the reducing agent, if the 

 solution is dilute. But it was not known until the experi- 

 ment of Mr. Daintree, and the following ones made by Mr. 

 Wilkinson, that this deposit would take place on a nucleus, 

 and be continued as long as gold remained in solution. If 

 this action went on in the drifts, it would account for the 

 greater purity of the gold aud for the nucleus of brown iron 

 ore so often found in nuggets and crystals. Strong solu- 

 tions of gold immediately begin to decompose the pyrites 

 and interfere with the regular deposition of gold. By a 

 strong solution, I refer to one containing more than one 

 grain of chloride of gold to the ounce of water. A weaker 

 solution than this also decomposes the pyrites, but so slowly 

 as not to interfere with the deposit taking place regularly ; 

 all the other sulphides are also decomposed. In the 

 experiment in which galena was used as a nucleus, this 

 decomposition was best marked Somewhat more than a 

 year ago I placed a cube of galena in a solution of chloride 

 of gold, with free access of air, and put in organic matter: gold 

 was deposited as usual, in a bright metallic film, apparently 

 completely coating the cube. After a few months the film 

 burst along the edo-es of the cube, and remained in this 

 state with the cracks open, without any further alteration in 

 size or form being apparent. Upon removing it from the 

 liquid a few days ago, and breaking it open, I found that a 

 large portion of the galena had been decomposed, forming 

 chloride and sulphate of lead, and free sulphur which were 

 mixed together, encasing a small nucleus of undecomposed 

 sulphate of lead. The formation of these salts had exerted 

 sufficient force to burst open the gold coating — which upon 

 the outside had the mammillary form noticed by Mr. Vv 7 il- 

 kinson, while the inside was rough and irregular, with 

 crystals forcing their way into the lead salts. 



Had this action continued undisturbed, the result would 

 have been a nugget with a nucleus of lead salts, or if there 

 had been a current to remove the results of the decomposi- 

 tion ; a nugget without a nucleus of foreign matter. If, 

 instead of galena, we had had a piece of pyrites to start 

 with, the decomposition would have gone on in the same 

 way, but the result would have been brown iron ore in 



