As with silver assays, if too much be employed, it will produce a loss, while too little would not extract all the copper.

The lead is first placed in the cupel, (fig. 2,) and only when the process of oxidation has commenced, is the paper containing the gold and silver to be added. The rest is performed exactly as with gold ores. The button should be hammered to a very thin sheet, before being submitted to the nitric acid; and to do this well, it should be perfectly cold, as otherwise marginal

cracks are often produced, which again may be productive of loss.

It may not be quite out of place here to give the contents of pure gold in carats fine, and the weight and value of the United States gold coins, as well as of those of other nations, made legal tender with us, according to the act of Congress of June, 1834. By an act of that date, the standard value of our eagles, and other gold coins in proportion, was changed; as will be seen from the subjoined table, which has been taken from the American Almanac of 1835, page 153.

Moidore, in proportion...... 6 22 152-2 21 33 6 55 7

XI.

To find the Proportion of Gold in a mixture of Gold and Quartz by Calculation.*

THE specific gravity of gold
The specific gravity of quartz

= =

19.000

= 2.600

These numbers can be corrected when experiment shows the specific gravities to be different.

A. Ascertain the specific gravity of the mixture of gold and quartz.

be 8.067.

Suppose it to

B. Deduct the specific gravity of the

*This article is taken from J. A. Phillips's "Gold Mining and Assaying," (London, 1852,) p. 85, a work published since the first edition of this little volume, and one which, like the other productions of its author, it is needless more particularly to recommend to those who pay attention to the recent publications in this department of applied chemistry.

mixture from the specific gravity of the gold: the difference is the ratio of the quartz by volume:—

19.000 8.067 10.933

=

C. Deduct the specific gravity of the quartz from the specific gravity of the mixture the difference is the ratio of the gold by volume:

8.0672.600 = 5.467

D. Add these ratios together, and proceed by the rule of proportion. The product is the per-centage of gold by bulk :

10.933 +5.467 = 16.400

16.4 is to 5.467 as 100 is to 33.35

E. Multiply the per-centage of gold by bulk, by its specific gravity. The product is the ratio of gold in the mixture by weight:

33.35 × 19.00 = 633.65

F. Multiply the per-centage of quartz by bulk, by its specific gravity. The product