COPPER, SILVER, AND GOLD 445 



the upper soil, but more frequently along the banks of dried-tip water- 

 courses and running streams. The sand of many rivers contains, 

 however, a very small amount of gold, which it is not profitable to 

 work ; for example, that of the Alpine rivers contains 5 parts of gold 

 in 10,000,000 parts of sand. The richest gold deposits are those of 

 Siberia, especially in the southern parts of the Government of Yeniseisk, 

 the South Urals, Mexico, California, South Africa, and Australia, 

 and then the comparatively poorer alluvial deposits of many countries 

 (Hungary, the. Alps, and Spain in Europe). The extraction of the 

 gold from alluvial deposits is based on the principle of levigation ; the 

 earth is washed, while constantly agitated, by a stream of water, 

 which carries away the lighter portion of the earth, and leaves the 

 coarser particles of the rock and heavier particles of the gold, together 

 with certain substances which accompany it, in the washing apparatus. 

 The extraction of this washed gold only necessitates mechanical ap- 

 pliances, 31 and it is not therefore surprising that gold was known to 

 savages and. in the most remote period of history. It sometimes occurs 

 in crystals belonging to the regular system, but in the majority of cases 



51 But the particles of golcLare sometimes so small that a large amount is lost during 

 the washing. It is then profitable to have' recourse to the extraction by chlorine and 

 KCN (Note 80). 



In speaking of the extraction of gold the following remarks may not be out of 

 place: 



In California advantage is taken of water supplied from high altitudes in order to 

 have a powerful head of water, with which the rocks are directly washed away, thus 

 avoiding the greater portion of the mechanical labour required for the exploitation of 

 these deposits. 



The last residues of gold are sometimes extracted from sand by washing them with 

 mercury, which dissolves the gold. The sand mixed with water is caused to come into 

 contact with mercury during the washing. The mercury is then distilled. 



Many sulphurous ores, even pyrites, contain a small amount of gold. Compounds of 

 gold with bismuth, BiAuj, tellurium, AuTe 2 (calverite), &c., have been found, although 

 rarely. 



Among the minerals which accompany gold, and from which the presence of gold may 

 be expected, we may mention white quartz, titanic and magnetic iron ores, and also the 

 following, which are of rarer occurrence : zircon, topaz, garnet, and such like. The con- 

 centrated gold washings first undergo a mechanical treatment, and the impure gold 

 obtained is treated for pure gold by various methods. If the gold contain a considerable 

 amount of foreign metals, especially lead and copper, it is sometimes cupelled, like silver, 

 so that the oxidisable metals may be absorbed by the cupel in the form of oxides, but in 

 every case the gold is obtained together with silver, because the latter metal also is" not 

 oxidised. Sometimes the gold is extracted by means of mercury, that is, by amalgama- 

 tion (and the mercury subsequently driven off by distillation), or by smelting it with 

 lead (which is afterwasds removed by oxidation) and processes like those employed for 

 the extraction of silver, because, gold, like silver, does not oxidise, is dissolved by lead 

 and mercury, and is non-volatile. If .copper or any other metal contain gold and it be 

 employed as an anode, pure copper will be deposited upon the cathode, while all the 

 gold will remain at the anode as a slime. This method often amply repays the whole 

 cost of the process, since it gives, besides the gold, a pure electrolytic copper. 



