There is a remarkable mixture of native gold with silver occasionally found in Siberia, and known under the name of _electrum_. Its color is pale brass-yellow, passing into silver-white. It occurs in small plates and imperfect cubes, and possesses many of the characters of gold, but it consists only of 64 per cent. of that metal, and 36 per cent. silver. It is at once known by its low specific gravity, which does not exceed 12. Other mixtures of gold are (1) a _rhodium-gold_ found in Mexico, and containing 34 to 43 per cent. of rhodium, having a specific gravity of 15½-16·8, and a clear, dirty yellow color; and (2) a _palladium-gold_ (containing 9·85 per cent. palladium, and 4·17 per cent. silver) found in Brazil and elsewhere in South America, in small crystalline grains of pale yellow color. The auriferous ores of tellurium, including silver, have hitherto only been found in Transylvania. Their color is steel-gray, and they tarnish on exposure. The variety called graphic-gold, or graphic tellurium, consists of about 60 per cent. of tellurium, 30 per cent. gold, and 10 per cent. silver, and is worked chiefly as an ore of gold. Another variety, "yellow gold glance," yields somewhat less tellurium, gold and silver, and as much as 20 per cent. of lead. Having now explained at some length the more manifest characteristics of gold, namely, its color, hardness, and specific gravity, it is necessary, before explaining the mode of separating it from associated minerals, that we should here give some account of the behavior of this metal under the blowpipe, and when exposed to simple chemical tests. The assay of gold and its accurate analysis, we postpone for the present. The method of blowpipe analysis, although exceedingly useful, is not absolutely necessary in the case of gold, because of the many readier ways of determining the metal, but it seems advisable to state the appearances presented. All the varieties are readily fusible into a globule, which when the gold is pure, is unaltered by the continuance of the heat. In this respect it differs entirely from iron and copper pyrites, which, on being exposed to the flame, give off sulphur fumes and undergo considerable change. In the case of gold containing other metals, these, with the exception of silver; may generally be got rid of by continuing the heat in the exterior flame with the addition of a little nitre. Before the oxy-hydrogen blowpipe, the metal is volatilized in the form of a purple oxide.