618 SCIENCE PROGRESS 



Electrical Industry 



Owing to its relatively high electrical conductivity, the metal 

 aluminium is now playing an important and steadily growing 

 part in the distribution of electrical power. Taking the con- 

 ductance of a copper cable of unit cross section as ioo, 

 aluminium of the requisite purity has a conductance of 60, 

 the exact figure depending, as in the case of copper, upon the 

 purity of the metal and its physical state. To carry a given 

 amount of current, it is therefore necesary to take a bigger cable 

 if aluminium be used, the cross section required being \'66 that 

 of copper. At first sight this does not seem promising but 

 when it is remembered that the densities of aluminium and 

 copper are 271 and 8-95 respectively, it will be seen that the 

 weights of cable required to carry the same amount of current 

 will be 1 "66 x 271 = 4*49 in the case of aluminium and 

 1 x 8'95 = 8"95 in that of copper. In other words, half the 

 weight of aluminium will be required and as the cost depends 

 upon the weight and aluminium wire is little more expensive 

 than copper wire per ton, a very large saving in capital outlay 

 is effected by the use of aluminium instead of copper. In the 

 case of bare, overhead conductors, such as are largely used in 

 young countries to convey electrical energy, the full benefit of 

 this economy is felt and there are in addition one or two 

 subsidiary advantages such as the decreased cost of carriage 

 to the point where the power line is to be erected, usually in 

 remote parts to which the cost of carriage is heavy. On the 

 other hand, the strength of aluminium is only half that of 

 copper but as the area of the aluminium is r66 times that 

 of the copper line, the strength of the former is 0*5 x v66 = 0*83 

 of that of the former. In consequence the sag between two 

 poles or towers is greater where aluminium is used and the poles 

 have therefore to be somewhat higher. The general conclusion 

 to be drawn from these various considerations is very favourable 

 to aluminium at the prices ruling to-day for the transmission of 

 power by means of bare conductors. 



Aluminium has so far not been found advantageous in cases 

 in which small bare single wires are used, such as telephone and 

 telegraph circuits. The explanation is to be found in chemical and 

 mechanical rather than in electrical considerations. Aluminium, 

 when exposed to the atmosphere, undergoes superficial oxida- 



