Fig. 3.—Equilibrium Diagram, Cu-Zn Series.

The Properties of Copper.—The properties of the metal which render it of such service in the arts and industries are mainly its high electrical conductivity, its great ductility, malleability, and toughness, which enable it to be readily worked up into the different forms in which it is employed, its high thermal conductivity, and its resistance to the various agencies which lead to corrosion. These are consequently the properties to which close study is directed. Of perhaps still greater importance is a knowledge of the influence exerted upon these properties by the circumstances which usually attend working practice; such as, for example, the various common impurities, and the variations of temperature, as well as the previous mechanical and thermal treatment. These can only be indicated in general terms here, references to authorities on the different branches being given later.

TABLE III. —Influence of Impurities on the Electrical Conductivity.

Addicks.Johnson.
Impurity.
Per cent.		 Conductivity. Impurity.
Per cent.		 Conductivity.
Pure copper,..101 ..101
Copper with—
 Aluminium,0·00698·60·0199·7
0·10966·80·0298·8
0·73943·5....
 Antimony,0·00799·6....
0·02297·2....
0·04795·40·0596·9
 Arsenic,0·00499·6....
0·00796·8....
0·01393·20·0492·4
0·14062·30·0682·0
 Bismuth,0·02899·60·0195·7
0·04599·3....
 Cadmium,0·06299·5....
0·11399·1....
0·42796·1....
 Cobalt,....0·0592·0
 Gold,0·08998·90·0599·7
0·14998·4....
0·31796·4....
 Iron,0·04296·8....
0·04692·9....
0·06889·60·0998·8
 Lead,0·08399·1....
0·05298·70·06100·6
0·34798·3....
 Manganese,....0·0298·8
 Nickel,....0·0591·4
 Oxygen,0·020100·7 ....
0·050101·4 ....
0·100100·5 0·1099·8
 Phosphorus,0·0852·3 0·00498·5
 Platinum,....0·0293·6
 Silicon,0·00799·4 0·00499·7
0·04299·00·0198·4
 Silver,0·003100·5 ....
0·137100·0 0·0599·8
0·34098·3....
 Sulphur,0·053100·0 0·0198·5
0·13599·0....
0·23698·9....
 Tellurium,0·065100·4 ....
0·181100·2 ....
0·40598·7....
 Tin,0·05297·60·05100·5
0·09792·7....
0·29579·8....
 Zinc,0·04898·30·0298·5
0·09596·3....

Physical Properties.—The colour of copper is familiar, being a fine salmon pink. The appearance of the fractured surface is a useful guide in several respects as to the condition of the metal, and in the process of manufacture the refiner relies upon this appearance as an important criterion of the progress of the refining operation. Copper containing an excess of oxygen, for example, has a purplish-red colour and a coarse brick-like fracture; this is known as “dry copper,” and the metal is brittle and commercially useless when in that form. The ingot of dry copper is also characterised by a depression running along the surface. Tough copper (“tough-pitch”) the mechanically useful variety resulting from the furnace-refining operation, possesses a bright salmon-coloured fracture, finely granular to silky in appearance, whilst “overpoled copper,” also brittle and industrially valueless whilst in that condition, has a very light salmon-coloured fracture, and is more coarsely fibrous.

The melting point of copper is 1,083° C., and is slightly lowered by the small quantities of impurity usually present in commercial metal. Molten copper is of a pale apple-green colour. The boiling point under ordinary conditions is about 2,300° C. (1,700° C. in vacuo). The electrical conductivity is of much importance. Copper ranks second only to silver as a conductor, the relative conductivity of the best copper being about 98 compared with silver as 100. The resistance of 12 inches of pure copper wire, 0·001 inch in diameter, is 9·612 ohms. The conductivity of the metal is decreased by mechanical working, and it follows the general straight-line law connecting conductivity and temperature.

The effect of even small quantities of impurity on this property is very marked, so much so that only the purest varieties are suitable for electrical work, and for this reason electrolytic refining is often a necessary operation in the manufacture of copper intended for this purpose.

Table III. on preceding page, summarises the results of the work of Addicks and Johnson, and indicates the effects of small amounts of different impurities on the conductivity of the metal.

The notoriously destructive effect of arsenic on the conductivity is very apparent.

The influence of most of the common impurities is of a similar nature, and detailed investigations indicate that the effect is more or less progressive as the quantity increases—within the limits usually present in commercial metal. The results of Hiorns and Lamb’s experiments with reference to arsenic and antimony are indicated in Fig. 4.