The Formation of Gold Nuggets. 13 
as on the surface of the quartz, and also in a remarkable 
mammillary form. This was in the solution for a week. 
No. 3 contains iron pyrites and galena, on both of 
which the gold has deposited, so that you cannot now 
distinguish one sulphide from the other. It remained ina 
solution of one gr. of chloride to the ounce of water for eight 
days. 
nos 4 and 5 are similar specimens to the last mentioned, 
the same strength of solution being used; but they were 
only dipped half way into it, so that the immersed part 
coated with gold may be compared with the other half on 
which the pyrites remains unaltered. 
I may here remark that a weak solution produces more 
perfect results than a strong one; with the latter the sul- 
phides are partly decomposed, and the gold is covered with 
a dark brown powdery film, as you will observe in some of 
the above specimens. This film does not prevent the growth 
of the gold in the solution, and it may easily be rubbed off. 
Nos. 6 to 13.—Iron, copper, and arsenical pyrites, anti- 
mony, galena, molybdenite, zinc-blend, and wolfram were 
treated in the above manner with similar results. 
Brown iron ore and quartz covered with peroxide of iron 
were also tried in the same way, but the gold was deposited 
only as a fine metallic powder. 
In the above experiments a small chip of wood was em- 
ployed as the decomposing agent. In one instance I used a 
bit of leather. All through the wood and leather gold was 
disseminated in fine particles, and when cut through the 
characteristic metallic lustre is brightly reflected. 
The first six of these sulphides were also operated upon 
simply in the solution without organic matter, but they re- 
mained unaltered. 
Iron pyrites was tried with metallic copper, zinc and iron 
as decomposing agents ; but metallic gold was deposited only 
as a fine powder, which settled at the bottom of the 
vessel. 
From these experiments it would appear that organic 
matter is the necessary chemical agent to decompose a solu- 
tion of the chloride of gold in order to precipitate the gold 
as a coherent coating around a nucleus presented to it; and 
that so far as we have yet tried, iron, copper, and arsenical 
pyrites, galena, antimony, molybdenite, blend, wolfram, and 
metallic gold, constitute especially favourable nuclei to de- 
monstrate this chemical reaction. 
