COPPER, SILVER, AND GOLD 443 



sodium thiosulphate, &c. Just as copper forms a link between the iron 

 metals and zinc, and as silver unites the light platinum metals with 

 cadmium, so also gold presents a transition from the heavy platinum 

 metals to mercury. Copper gives saline compounds of the types CuX 

 and CuX 2 , silver of the type AgX, whilst gold, besides compounds of- 

 the type AuX, very easily and most frequently forms those of the type 

 AuCl 3 . The compounds of this type frequently pass into those of the 

 lower type, just as PtX 4 passes into PtX 2 , and the same is observable 

 in the elements which, in their atomic weights, follow gold. Mercury 

 gives HgX 2 and HgX, thallium gives T1X 3 and T1X, lead gives 

 PbX 4 and PbX 2 . On the other hand, gold in a qualitative respect 

 differs from silver and oopper in the extreme ease with which all its com- 

 pounds are reduced to metal by many means. This is not only accom- 

 plished by many reducing agents, but also by the action of heat. Thus 

 its chlorides and oxides lose their chlorine and oxygen when heated; 

 and, if the temperature be sufficiently high, these elements are entirely 

 expelled and metallic gold alone remains. Its compounds, therefore, 

 act as oxidising agents. 29 



In nature gold occurs in the primary and chiefly in quartzose rocks, 

 and especially in quartz veins, as in the Urals (at Berezoffsk), in 

 Australia, and in California. The native gold is extracted from these 

 rocks by subjecting them to a mechanical treatment consisting of 

 crushing and washing. 29 Ws Nature has already accomplished a similar 



* Heavy atoms and molecules, although they may present many points of analogy, are 

 more easily isolated ; thus CigH^, although, like C 2 H 4 , it combines with Br 2 , and has a 

 similar composition, yet reacts with much greater difficulty than C 2 H 4) and in this it resem- 

 bles gold ; the heavy atoms and molecules are, so to say, inert, and already saturated by 

 themselves. Gold in its higher grade of oxidation, Au 2 O3, presents feeble basic pro- 

 perties and weakly-developed acid properties, so that this oxide of gold, Au 2 O 3 , may be 

 referred to the class of feeble acid oxides,, like platinic oxide. This is not the case in the 

 highest known oxides of copper and silver. But in the lower grade of oxidation, aurous 

 oxide, AujO, gold, like silver and copper, presents basic properties, although they ar^ 

 not very pronounced. In this respect it stands very close in its properties, although 

 not in its types of combination (AuX and AuX 3 ), to platinum (PtX 2 and PtX 4 ) and its 

 analogues. 



As yet the general chemical characteristics of gold and its compounds have not been 

 fully investigated. This is partly due to the fact that very few researches have been 

 undertaken on the compounds of this metal, owing to its inaccessibility for working 

 in large quantities. As the atomic weight of gold is high (Au = 197), the preparation of 

 its compounds requires that it should be taken in large quantities, which forma ah 

 obstacle to its being fully studied. Hence the facts concerning the history of this metal 

 are rarely distinguished by that exactitude with which many facts have been established 

 concerning other elements more accessible, and long known in use. 



Wbl Sonstadt (1872) showed that sea water, besides silver, always contains gold, 

 Munster (1892) showed that the water of the Norwegian fiords contains about 5 milli- 

 grams of gold per ton (or 5 milliardths) i.e a quantity deserving practical attention, and 

 I think it may be already said that, considering the immeasurable amount of sea water, 

 in time means will be discovered for profitably extracting gold from eea water by 



