ORIGIN OF GOLD NUGGETS. 315 
processes of extraction, and some, although a smaller amount, is 
almost certain to be obtained by each successive treatment, more- 
over the material becomes more broken up by the further handling 
and weathering, and more gold is thus set free both mechanically 
and probably by chemical changes also. 
He then cites, page 64, experiments of his own similar to 
Wilkinson’s, Newbery’s, and many others, to show that gold is 
precipitated from its solution as chloride by petroleum, cork, peat, 
leather, leaves, &c. The petroleum threw down long crystals of 
gold resembling Chester’s hexagonal crystals, and the peat a 
mammillary mass resembling the form of nuggets. 
He then tried, p. 65, the solubility of gold in solutions of salts ; 
ammonium sulphate and chloride, potassium chloride and bromide 
placed in sealed tubes with spongy gold for eight months gave no 
reaction ; on heating them for five hours at 150° to 200° ©. only 
the potassium bromide gave a reaction. 
Pure sponge gold was sealed up for three months with ammon- 
ium sulphide with no reaction; but both potassium and sodium 
sulphides gave black precipitates and a strong reaction for gold 
was given by the: liquid in each case; the ammonium sulphide 
heated for six and a-half hours at 145° to 180° C. was unchanged 
but reacted strongly for gold ; the solution of potassium sulphide 
also reacted and the glass was much attacked, further there wasa 
black precipitate of gold ; the sodium sulphide acted much more 
feebly. Other salts and solvents were used but with no very 
striking results. 
He states, p. 72, that, ‘‘the same conditions which cause the 
solution of the gold in certain cases cause also the solution of the 
silica.” And ‘many of the causes which produce the precipitation 
of the gold would also cause the reduction of soluble sulphates to 
insoluble sulphides, the gold being retained within the mass. This. 
would account for the almost constant presence of gold in pyrites.” 
“No single agent is so powerful a solvent of gold as chlorine. 
Very few drainage waters are free from some compound of it, and 
