COPPEB, SILVER, AND GOLD 415 



colour of the latter to a considerable degree / with a certain amount of 

 zinc the colour of the copper becomes yellow, and with a still larger 

 proportion of zinc an alloy is formed w hich has a greenish tint In those 

 alloys of zinc and copper which contain a larger Amount of zine than 

 of copper, the yellow colour disappears and is replaced by a greyish 

 colour. But when the amount of zinc is diminished to about 20 p.c.j 

 the alloy is red and hard, and is called ' tombac.' A contraction takes 

 place in alloying copper with zinc, so that the volume of the alloy is 

 less than that of either metal individually. The zinc volatilises on 

 prolonged heating at a high temperature and the excess of metallic 

 copper remains behind. When heated in the air, the zinc oxidises 

 before the copper, so that all the zinc alloyed with copper may be 

 removed from the copper by this means. An important property of 

 brass containing about 30 p.c. of zinc is that it is soft and malleable in: 

 the cold, but becomes somewhat brittle when heated. We may also 

 mention that ordinary copper coins contain, in order to render them 

 hard, tin, zinc, and iron (Cu = 95 p.c.) ; that it is now customary to add 

 a small amount of phosphorus to copper and bronze, for the same pur- 

 pose ; and also that copper is added to silver and gold in coining, &c. 

 to render it hard ; moreover, in Germany, Switzerland, and Belgium, 

 and other countries, a silver- white alloy (melchior, German silver, &c.), 

 for base coinage and other purposes, is prepared from brass and nickel 

 (from 10 to 20 p.c. of nickel ; 20 to 30 p.c. zinc ; 50 to 70 p.c. copper), 

 or directly from copper and nickel, or, more rarely, from an alloy con- 

 taining silver, nickel, and copper. I2bis 



Copper, in its cuprous compounds, is so analogous to silver, that 



taining 45-80 p.c. Cu crystallise in cubes if slowly cooled (Bi also gives crystals). By 

 washing the surface of brass with dilute sulphuric acid, Zn is removed and the article 

 acquires the colour of copper. The alloys approaching Zn^Cuj in their composition 

 exhibit the greatest resistance (under other equal conditions ; of purity, forging, rolling, 

 &c.) The addition of 3 p.c. Al, or 5 p.c. Sn, improves the quality of brass. Bespecting 

 aluminium bronze see Chapter XVII. p. 88. 



12 bte Ball (also Kamensky), 1888, by investigating the electrical conductivity of the 

 alloys of antimony and copper with lead, came to the conclusion that only two definite 

 compounds of antimony and copper exist, whilst the other alloys are either alloys of these 

 two together or with antimony or with copper. These compounds are Cu 2 Sb and 

 Cu 4 Sb one corresponds with the maximum, and the other with the minimum, electrical 

 resistance. In general, the resistance offered to an electrical current forms one of the 

 methods by which the composition of definite alloys (for example, Pb a Zn 7 ) is often 

 established, whilst the electromotive force of alloys affords (Laurie, 1888) a still more 

 accurate method for instance, several definite compounds were discovered by thia 

 method among the alloys of copper with zinc and tin ; but we will not enter into any 

 details of this subject, because we avoid all references to electricity, although the reader 

 is recommended to make himself acquainted with this branch of science, which has many 

 points in common with chemistry. The study of alloys regarded as solid solutions should, 

 in my opinion, throw much light upon the question of solutions, which is still obscure .- 

 in many aspects and in many branches of chemistry. 

 *G 



