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With the development of analytical chemistry, the blowpipe method has given way to the “wet” method once more, but this is not very suitable or useful to the gemologist as it is often restricted to minerals which are soluble in some liquid. A recent method is the noting of calorimetric reactions in the presence of a variety of reagents. By these means, a drop of the reagent selected is allowed to come into contact with a drop of the solution ‘being tested, and the resulting color is sufficient to indicate which elements are present. The method in use and the reagents required are described in a paper read by J. H. Watson on November 1st 1934, before the Mineralogical Society of London. The details do not come within the scope of this work, nor would the results be of much practical use to the gem dealer or collector.

Actually, an analysis of the earth’s crust, based on a series of averages taken, shows that oxygen and silicon make up the major portion. These elements are, of course, found in chemical combination with others, but nearly half the weight is oxygen, while more than a quarter is silicon. Silicon, iron, aluminum, and magnesium exist in large quantities, the proportions being about 46 per cent oxygen, 27 per cent silicon, 8 per cent aluminum, 5 per cent iron, 4 per cent calcium, and 3 per cent potassium, other elements making up the remainder. Almost all the minerals are found in combination with others, the rough material being known as ores, and from these the single mineral or metal must be extracted. Gem stones are not extracted, except by simple separation, from ores. They are found as we know them, with the exception of shaping and polishing which has been applied to improve their beauty.

At present, about 92 different stable elements are known, and all minerals are composed of one or more of these elements. For conciseness, these elements are generally denoted by a symbol, e.g. C for carbon, Al for aluminum, Mg for magnesium, and the chemist has a simple means of showing not only the constituent elements of a substance by such symbols but also their compara tive weights.
Elements combine in definite proportions only, and each proportion is a definite character of that element, which is called its atomic weight. For instance, the atomic weight of hydrogen is 1, of carbon 12, of oxygen 16, and of magnesium 24. Certain gases and substances are capable of forming acids in conjunction with hydrogen, or hydrogen and oxygen. These acids combine with greater or less avidity with other elements which do not form acids, and which are termed bases. Such a combination of an acid with a base produces a compound solution called a salt. All the salts whose names terminate in “ide,” such as fluorides, sulphides, etc., are simply combinations of a non-metallic element with a metal.