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Gravimetric methods are divided into three groups: (1) mechanical separations; (2) dry methods; and (3) wet methods. ~Mechanical Separations.~--Under this head are classed the method of assaying tin ores, known as vanning, and the amalgamation assay for gold. A set of sieves to determine the relative proportion of powders of different degrees of fineness is sometimes useful. A set with 10, 20, 40 and 80 meshes to the inch is convenient. ~Dry Assays.~--An important distinction between wet and dry methods of assaying is, that in the former the substance is got into the liquid state by solution, whilst in the latter fusion is taken advantage of. The difference between solution and fusion is easily illustrated: a lump of sugar heated over a candle-flame melts or fuses; suspended in water it dissolves. Many substances which are insoluble or infusible of themselves, become soluble or fusible when mixed with certain others; thus, in this way, solution is got with the aid of reagents, and fusion with the help of fluxes. For example, lead is insoluble in water, but if nitric acid be added, the metal rapidly disappears. It is convenient, but somewhat inaccurate, to say that the acid dissolves the lead. If the lead be acted on by nitric acid alone, without water, it is converted into a white powder, which does not dissolve until water is added; in this case it is obvious that the water is the solvent. The function of the acid is to convert the lead into a soluble compound.

The Argus is a bird with magnificent plumage; it inhabits the forests of Java and Sumatra, and takes its place beside the pheasant, from which it only differs in being unprovided with spurs, and by the extraordinary development of the secondary feathers of the wings in the male. The tail is large and round, and the two middle feathers are extremely long and quite straight. When paraded, as it struts round the female, spreading its wings and tail, this bird presents to the dazzled eye of the spectator two splendid bronze-colored fans, upon which is sprinkled a profusion of bright marks much resembling eyes. It owes its name of Argus to these spots.

The opening up of these Catacombs has brought to light many most interesting relics of primitive Christianity. In these Christian cemeteries and places of worship there are signs not only of the deep emotion and hope with which they buried their dead, but also of their simple forms of worship and the festive joy with which they commemorated the Nativity of Christ. On the rock-hewn tombs these primitive Christians wrote the thoughts that were most consoling to themselves, or painted on the walls the figures which gave them the most pleasure. The subjects of these paintings are for the most part taken from the Bible, and the one which illustrates the earliest and most universal of these pictures, and exhibits their Christmas joy, is "The Adoration of the Magi."

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