_The Specific Gravity_.--In ascertaining the specific gravity the following apparatus is necessary: a small pair of hand scales with a set of weights, from one grain to one ounce. These can be procured from the apparatus maker, the scales for about fifty cents, and the weights for not much over the same amount. The scales are prepared for this work by cutting two small holes in one of the scale pans, near together, with a pointed piece of metal, and tying a piece of silk thread about eight inches long into these. In a loop at the end of this thread the mineral to be examined is suspended. It should be a pure representative of the mineral it is taken from, should weigh about from one hundred grains to an ounce, and be quite dry and free from dirt. If the piece of mineral obtained is very large, this sized portion may be often taken from it without injury; but it will not do to mar the beauty of a mineral to ascertain its specific gravity, and it is generally only applicable when a small piece is at hand. With more weights, however, a piece of a quarter pound weight may be taken if necessary. The mineral is tied into the loop and weighed, the weight being set down in the note book, either in grains or decimal parts of an ounce. Call this result A. It is then weighed in some water held in a vessel containing about a quart, taking care while weighing it that it is entirely immersed, but at the same time does not touch either the sides or bottom. Both weighings should be accurate to a grain. This result we call B. The specific gravity is found by subtracting B from A, and dividing A by the remainder. For instance, if the mineral weighed eight hundred grains when weighed in the air, and in the water six hundred, giving us the equation: 800 / (800 - 600) = sp. gr., or 4, which is the specific gravity of the mineral. If the mineral whose specific gravity is sought is an incrustation on a rock, or a mixture of a number of minerals, or would break to pieces in the water, the specific gravity is by this method of course unattainable, and other data must be used.