It is merely necessary to enumerate some few of the present aspects of electrical industry in order to realise the enormous absorption of copper in this connection, as, for instance, electrical traction, lighting, and power, the telegraph, and the telephone. With reference to the use of the metal for this work, it is important that certain mechanical as well as electrical requirements should be fulfilled, for in many branches, considerable strength of the material is also requisite. The demand of the electrical engineer is that as a conductor, the copper shall offer a minimum of resistance to the passage of the current, and for this requirement the metal must be in a condition of very great purity. With but few exceptions, this necessitates the purification of the copper by electro-deposition. Electro-deposited metal as produced at the refineries is, however, not immediately suitable for drawing into wire, owing to the weakness and porosity inherent in the material prepared by this method. It must, therefore, be melted, brought to pitch, cast into bars, and these bars transformed into wire, which operations require to be conducted with much care in order to keep the metal in as pure a condition as possible for its work. It may be noted that within recent years, several processes, notably those of Cowper-Coles and Elmore, have been put into operation for the direct manufacture for electrical purposes, of electrolytic-copper wire of the requisite strength. The mechanical qualities demanded of the metal for such purposes as telegraph work may be indicated by the two specifications of wire for the British Post Office, which are appended:— A. _Post Office Specification._ =Weight=, 150 lbs. per mile. =Minimum diameter=, ·95½". =Maximum diameter=, ·98".[1] =Minimum breaking strain=, 490 lbs. =Minimum number of twists=, 25 in 3 inches. =Wraps required=, 6 times round wire of its own diameter, unwrapped, and again wrapped without breaking. =Maximum resistance per mile at= 60° =F.=, 5·857 ω. B. _Post Office Specification._ =Weight=, 500 lbs. per mile. =Minimum diameter=, ·135¼". =Maximum diameter=, ·138¾". =Minimum breaking strain=, 950 lbs. =Minimum number of twists=, 30 in 6 inches. =Wraps required=, 6 times round wire of its own diameter, unwrapped, and again wrapped without breaking. =Maximum resistance per mile at= 60° =F.=, 2·928 ω. The following figures afford some indication of the increasing demand for copper in two branches only of electrical industry:— 1902. 1907. Mileage of wire for telegraph purposes, 3·9 5·3 " " telephone purposes, 10·9 28·2 (in million of miles)