NOBLE METALS.
These are so called because they retain their brilliancy and are not easily affected by other substances. Three of them are specially important: gold, silver and platinum. Gold is mentioned in the second chapter of Genesis: “and the gold of that land is good.” Although constituting an inconsiderable part of the earth, it is much more widely distributed than many suppose, but often exists in such small quantities that its production is not profitable.
Australia and California are the gold lands. It is found principally in three situations: in sands which have been washed from the mountains, in little pockets in the rocks, and in veins of quartz. From the first it is separated by simply washing away the lighter materials, from the last situation it is procured by quarrying the rock, crushing it with stamping machines, then washing with water to remove the pulverized quartz, and gathering up the powdered gold with quicksilver. The mercury is removed by vaporizing. Gold is nineteen times heavier than water, extremely ductile, and the most malleable of all substances. Silver is abundant in the mountains of the west. It is usually found in the form of black sulphide (Ag₂S) or horn-silver (AgCl). When unpolished it is perfectly white, and is called dead or frosted silver. All are familiar with the properties of this attractive metal. Just now its producers in Colorado seem to fear its displacement from its important position in the coinage of the country. In nitrate of silver (AgNO₃) we have a material that perpetuates the faces of our friends, many a goodly landscape, and marvelous picture.
MAGNET GATHERING IRON FILINGS.—A MAGNET WILL ALSO ATTRACT NICKEL FILINGS.
Platinum stands at the extreme limit of the elementary world in point of weight, being twenty-one and fifty-three hundredths times heavier than water. Russia has almost a monopoly of the production of this metal. It is about the value of gold, and to the chemist is of immense importance, on account of its high point of fusibility, which is over 4,000°. It is so ductile that it can be drawn out into wire so fine as to be invisible to the naked eye. This microscopic wire is used for centering the field of view in the finest telescopes.