chloride disappeared,
and in half an hour the fluid turned blue, and a gelatinous dark-blue
precipitate appeared and adhered to the sides of the vessel. In a
few days moss-like forms were seen on the surface of the precipitate,
presumably approximating to what we know as dendroidal gold--that
is, having the appearance of moss, fern, or twigs. After allowing the
precipitate to remain undisturbed under water for a month or two a
decomposition took place, and in the silicate of gold specks of metallic
gold appeared. From this, the Professor argues, and with good show of
reason, that as we know now that the origin of our quartz lodes was
the silicates contained in certain rocks, it is probable that a natural
silicate of gold may be combined with these silicates. If this can be
demonstrated, the reason for the almost universal occurrence of gold in
quartz is made clear.

About 1870, Mr. Skey, analyst to the New Zealand Geological Survey
Department, made a number of experiments of importance in respect to
the occurrence of gold. These experiments were summarised by Sir James
Hector in an address to the Wellington Philosophical Society in 1872.
Mr. Skey's experiments disproved the view generally held that gold is
unaffected by sulphur or sulphuretted hydrogen gas, and showed that
these elements combined with avidity, and that the gold thus treated
resisted amalgamation with mercury. Mr. Skey proved the act of
absorption of sulphur by gold to be a chemical act, and that electricity
was generated in sufficient quantity and intensity during the process
to decompose metallic solutions. Sulphur in certain forms had long been
known to exercise a prejudicial effect upon the amalgamation of gold,
but this had always been attributed to the combination of the sulphur
with the quicksilver used. Now, however, it is certain that the
sulphurising of the gold must be taken into account. We must remember
that the particles of gold in the stone may be enveloped with a film
of auriferous sulphide, by which they are protected from the solvent
actions of the mercury. The sulphurisation of the gold gives no ocular
manifestation by change of colour or perceptible increase of weight,
as in the case of the formation of sulphides of silver, lead and other
metals, on account of the extremely superficial action of the sulphur,
and hence probably the existence of the gold sulphide escaped detection
by chemists.

Closely allied to this subject is the in