convenient
place in a river is selected where there is a good current, not too
deep, and where, if possible, there are no large bowlders. A low fence
or dam is generally built from the sides part way across the stream to
increase the flow of water. The men—half a dozen or more are
needed—stand in a row facing upstream and rake up the gravel above them
with a special long-handled "mamoty" (sort of hoe or rake). They work
as far up as their "mamoties" will reach, and eventually scoop a large
hole under water in front of them. By this process the overlying layers
of sand and clay are removed and the illam exposed. This gravel, along
with that underneath, is then worked up and allowed to drop in the
water near the men's feet, where the current washes away the lighter
material. The gravels thus partly concentrated are washed in the usual
way in baskets.
SIMPEE METHOD OF TESTING PRECIOUS STONES.
Mr.
Meyer D. Rothschild" has suggested a simple test, applicable to a
number of stones, that can be made by any jeweler who will exercise
care in its execution. Hydrofluoric acid or "white acid"' (a mixture of
ammonia and hydrofluoric acid) is used. The acid should never be
allowed to come in contact with the skin, as it is very poisonous and
highly corrosive, producing painful sores and ulcers. The stone to be
tested is handled with forceps and immersed one minute in the acid;
then it is removed and the acid is washed off. The test is applicable
only to diamond, ruby, sapphire, spinel, emerald, aquamarine, precious
topaz, tourmaline, garnet, and kunzite, which are unaffected by the
hydrofluoric acid. The test is not applicable to turquoise and opal,
which are rapidly etched or eaten away by this acid, nor to peridot and
the quartz gems, as amethyst, false topaz, crystal, agate, etc., which
have their surfaces dimmed and require repolishing. The genuine
reconstructed and artificial ruby is also unaffected, while all
imitations made of paste, as imitation ruby, sapphire, emerald, etc.,
are rapidly attacked.
PRODUCTION.
It
has been found next to impossible to obtain definite figures showing
the production of many varieties of gem minerals in 1906. There has
doubtless been a production of several gem minerals not recorded in the
table, but since no information could be obtained concerning them, they
have not been listed. There are several causes combining to make the
collection of statistics for precious stones difficult. In many cases
the production is made up of a number of small lots and scattered finds
which are brought in at different times and disposed of to different
people. Often the persons interested in mining gems do not care to
furnish figures showing the production, which has then to be either
estimated or omitted entirely. There have been, however, a great many
producers and men interested in minerals who have generously assisted
in every way possible toward the compilation of statistics of
production and have furnished information concerning the progress of
the industry.
It
has been deemed advisable, for several reasons, to make a change in the
form of table showing the production of precious stones. First,
