42 TlMEHRI. 
rob a sluice, which it appears is frequently done. Dip 
a silver spoon into the mercury, then stir up with it the 
stuff lying above the cross riffles, and when the spoon is 
well loaded with amalgam, wipe it off with finger and 
thumb, and proceed as before. Like samphire gathering, 
it is, however, a dangerous trade, for when taken the 
thief is not only well shaken but often strung up. 
Complete and rapid amalgamation only occurs when 
perfectly clean gold is exposed to the action of pure 
quicksilver. The fact of gold being alloyed with other 
metals does not prevent this if its surface is bright. 
Often, however, gold found in placer mines is slightly 
tarnished by oxidation of the alloy, and amalgamation is 
hindered. In California, much of the placer gold is 
wholly or partly coated with silica cemented by sesqui- 
oxide of iron — if entirely so coated, mercury has no 
action on it — and if this rusty gold, as it is termed, has 
its iron coat dissolved by means of hydrochloric acid, the 
silica easily drops off and amalgam is easily formed. 
The treatment of rusty gold was described in a 
Report of the State Mineralogist for 1880, which is not 
included in those sent to the Society. From a paper 
read in 1874 before the Royal Society of New South 
Wales, it appears that the best mode of destroying the 
mineral compounds, which by enveloping the gold pre- 
vented the action of mercury upon it, was by roasting in 
a furnace devised for this purpose. The resulting 
sand is made damp and ground with an equal weight of 
mercury for § hour, under an ordinary Chilian mill — the 
finely ground sand being carried off by a stream of 
water to the f( concentrator," leaving the amalgam in the 
mill. Fresh sand is passed through the mill until 
