416 PRINCIPLES OF CHEMISTKY 



were thefe* no cupric compounds, or if silver gave stable compounds 

 of the higher oxide, AgO, the resemblance would be as close as that 

 between chlorine and bromine or zinc and cadmium ; but silver 

 compounds corresponding to AgO are quite unknown. Although 

 silver peroxide which was regarded as AgO, but which Berthelot 

 ^1880) recognised as the sesquioxide Ag 2 O 3 is known, still it does 

 not form any true salts, and consequently cannot be placed along 

 with cupric oxide. In distinction to copper, silver as a metal does 

 not oxidise under the influence of heat ; and its oxides, Ag 2 O and 

 Ag 2 O 3 , easily lose oxygen (see Note 8 tri). Silver does not oxidise in 

 air at the ordinary pressure, and is therefore classed among the 

 so-called noble metals. It has a white colour, which is much purer 

 than that of any other known metal, especially when the metal is chemi- 

 cally pure. In the arts silver is always used alloyed, because chemi- 

 cally-pure silver is so soft that it wears exceedingly easily, whilst when 

 fused with a small amount of copper, it becomes very hard, without 

 losing its colour. 13 



15 There are not many soft metals ; lead, tin, copper, silver, iron, and fold are some- 

 what soft, and potassium and sodium very soft. The metals of the alkaline earths 

 are sonorous and hard, and many other metals are even brittle, especially, bismuth 

 and antimony. But the very slight significance which these properties have in 

 determining the fundamental chemical properties of substances (although, however, of 

 immense importance in the practical applications of metals) is seen from the example 

 shown by zinc, which is hard at the ordinary temperature, soft at 100, and brittle 

 at 200. 



As the value of silver depends exclusively on its purity, and as there is no possibility, 

 of telling the amount of impurities alloyed with it from its external appearance, it is 

 customary in most countries to mark an article with the amount of pure silver ifc contains 

 after an accurately-made analysis known as the assay of the silver. In France the 



FJG. 95. Cupel for silver assaying. FIG. 96. Clay muffle. 



assay of silver shows the amount of pure silver in 1,000 parts by weight ; in Russia the 

 amount of pure silver in 96 parts that is, the assay shows the number 'of zolotniks 

 (4'26 grams) of pure silver in one pound (410 grams) of alloyed silver. Russian silver is 

 generally 84 assay that is, contains 84 parts by weight of pure silver and 12 parts of 

 Copper and other metals. French money contains 90 p.c. (in the Russian system this 

 Will be 86'4 assay) by weight of silver [English coins and jewellery contain 92'5 p.c. of 

 silver] ; the silver rouble is of 83 assay that is, it contains 86'8 p.c. of silver and the 

 smaller Russian silver coinage is of 48 assay, and therefore contains 50 p.c. of silver. 

 Silver ornaments and articles are usually made in Russia of 84 and 72 assay. As 

 the alloys of silver and copper, especially after being subjected to the action of heat, are 

 not so white as pure silver, they generally undergo a process known as ' blanching ' (or 



