GOLD. 325 



Luna ; gold, Sol ; lead, Saturn ; iron, Mars ; quicksilver, Mercury ; and capper, 

 Venus. The crystallization of tin may be recognised also by rubbing a piece 

 of this metal with hydrochloric acid ; the fragments thus rubbed off exhibit 

 specimens of branching crystals similar to the hoar-frost which we see in 

 severe winter weather. If we bend a rod of tin in our hands the crystals 

 break, with a peculiar rustling sound. 



When speaking of precious metals, we may call to mind that the alche- 

 mists considered gold as the king of metals, and the other valuable ones as 

 noble metals. This definition is erroneous, if we look upon the useful as the 

 most precious ; for, in that case, iron and copper would be placed in the 

 first rank. If gold were found abundantly on the surface of the soil, and 

 iron was extremely rare, we should seek most eagerly for this useful metal, 

 and should despise the former, with which we can neither make a plough- 

 share nor any other implement of industry. Nevertheless, the scarcity of 

 gold, its beautiful yellow colour, and its unalterability when in contact with 

 air, combine to place it in the first rank in the list of precious metals. Gold 

 is very heavy ; its density is represented by the figure 19-5. It is the most 

 malleable and the most ductile of metals, and can be reduced by beating to 

 such thin sheets that ten thousand can be laid, one over the other, to obtain 

 the thickness of a millimetre. With a grain of gold a thread maybe manu- 

 factured extending a league in length, and so fine that it resembles a spider's 

 web. When gold is beaten into thin sheets it is no longer opaque ; if it is 

 fastened, by means of a solution of gum, on to a sheet of glass, the light 

 passes right through it, and presents a very perceptible green shade. Gold 

 is sometimes found scattered in sand, in a condition of impalpable dust, and, 

 in certain localities, in irregular lumps of varying size, called nuggets. Gold 

 is the least alterable of the metals, and can be exposed, indefinitely, to the 

 contact of humid atmosphere without oxidizing. It is not acted on by the 

 most powerful acids, and only dissolves in a mixture of nitric acid and hydro- 

 chloric acid. We can prove that gold resists the influence of acids by the 

 following operation : 



Some gold-leaf is placed in two small phials, the first containing hydro- 

 chloric acid, and the second nitric acid. The two vessels are warmed on 

 the stove, and whatever the duration of the ebullition of the acids, the gold- 

 leaf remains intact, and completely resists their action. If we then empty 

 the contents of one phial into the other, the hydrochloric and nitric acids 

 are mixed, and we see the gold-leaf immediately disappear, easily dissolved 

 by the action of the liquid (aqua regia). Gold also changes when in contact 

 with mercury; this is proved by suspending some gold-leaf above the surface 

 of this liquid (fig. 316); it quickly changes, and unites with the fumes of the 

 mercury, becoming of a greyish colour. 



Silver is more easily affected than gold, and though so white when 

 fused, tarnishes rapidly in contact with air. It does not oxidize, but 

 sulphurizes under the influence of hydro-sulphuric emanations. Silver 

 does not combine directly with the oxygen of the atmosphere ; but under 



