the weight of the buttons of impure gold, and about half the weight of both in pure lead, should be melted up with them in one crucible, (fig. 2, Plate II.) This single button of gold and silver alloy is to be hammered flat on a little steel anvil, and slightly curved, as this shape will allow it more easily to pass through the mouth of a little vial, in which it is now placed to be boiled with nitric acid 2 drams) of from 1 to 3 specific gravity. The vial should be round at the bottom as this is performed over a spirit-lamp. We allow the liquid to boil until the yellowish vapours of nitrous acid gas have ceased to be emitted. The gold is then pure, and requires only to be boiled a couple of times in water to remove the acid, and then to be heated to redness to evaporate the water, to enable us to weigh it, which, as with all other assays, should never be done till the metal is perfectly cold.

If a small portion of platinum be in the ore, it will be found in the nitric acid solution of silver. (See Platinum.)

The original amount of silver may be ascertained by deducting the weight of the gold from the button produced before the other pure silver was added.

VI.

Assay of Gold Ores by Amalgamation.

THIS method is founded on the fact, that gold unites with quicksilver to form an amalgam, for thus the alloys of mercury and other metals are termed. It is one that may answer for peculiar circumstances, though it is not accurate enough to serve as a regular dokimastic* test, since lead and silver also produce amalgams.

We require pure mercury for this purpose; and as the quicksilver of commerce generally contains some lead, we must purify it by pressing it through a piece of buckskin.

The powdered gold ore, which ought

* A technical term, derived from the Greek verb Sozuale, to try, to test the purity of a thing.

first to be reduced in volume by washing, is brought in contact with the quicksilver, the sand or gangue-rock removed by sifting the mass through a coarse cloth; after which, by forcing the quicksilver through some buckskin, the amalgam is retained.

By evaporating the mercury in an iron spoon over a lamp, the gold is procured, which will, however, still be found to contain silver or lead, if these occur in the

ore.

VII.

Assay of Gold by Washing.

THIS is a way of ascertaining the ap proximate value of a gold ore, which hardly deserves being called an assay, although, with an experienced hand, tolerable accuracy may be attained.

It is based on the fact, that gold is much heavier than quartz or other ganguerock, and therefore the rock should be well pounded for this operation.

The process is precisely the same as that used to extract gold from the sand of river beds, and which is now so extensively employed in California. Even the vessels used are frequently of the same kind, though it is better to have a small glass cylinder, about three times the length of the part that will be occupied by the ore,