GOLD EXTRACTION PROCESSES. 485 



expeditions have not been unknown in much later times, 

 and the method of obtaining gold by washing river sands 

 is still practised with improvements in matters of detail in 

 many parts of the world. Hides are even now occasionally 

 employed to catch the gold, but sheepswool when used is 

 generally in the form of blankets. 



The use of mercury as an aid in the collection of gold 

 contained in river sands or in crushed rock is also of great 

 antiquity. The earliest mention of quicksilver itself appears 

 to occur in the works of Theophrastus, about B.C. 300; but 

 Diodorus of Sicily, who saw gold being extracted from 

 quartz in Upper Egypt in the time of Julius Csesar does 

 not refer to its use. 1 Only a few years later, however, 

 Vitruvius, 2 about B.C. 13, described the manner in which, 

 by the help of quicksilver, gold was recovered from cloth 

 in which it had been interwoven, and in Pliny's time the 

 separation of gold from its impurities generally by the 

 same means was well known. 3 It is probable that this 

 knowledge was never afterwards entirely lost, although the 

 references to it in the Middle Ages are very scanty. For 

 example Geber 4 in the eighth century was aware that 

 mercury would dissolve considerable quantities of gold and 

 silver, but not earthy materials, and Theophilus the monk, 5 

 in the eleventh century carefully described the method of 

 washing the sands of the Rhine on wooden tables, the 

 final operation consisting in treating the concentrates with 

 quicksilver for the removal of the gold. Biringuccio 6 was 

 taught the secret of this use of mercury in Italy some time 

 before 1540 in return for the present of a valuable diamond 

 ring, and it is clear that the so-called invention of the 

 amalgamation process in Mexico by the Spaniards in 1557 



1 Diodor., iii., 13. A full translation is given by B. H. Brough in his 

 Cantor lectures on Mine Surveying. Juur. Soc. Arts, 1892. 

 2 Vit. lib., vii., cap. 8. 



3 Nat. Hist., lib. xxx., cap. vi., sect 32. Quoted in full in Percy's 

 Metallurgy of Silver and Gold, p. 559. 



4 Salmon's Geber, cap. 47. 5 Theophili, lib. iii., cap. 49. 

 6 De la Pirotechnia. Venetia, 1540. Lib. ix., cap. xi., fol. 142. 



