MODERN USES OF THE METAL ALUMINIUM 619 



tion but this ceases at a certain distance from the surface, the 

 coating formed acting protectively. In the case of large 

 conductors, corrosion does not proceed far enough to cause 

 any trouble, whereas the strength of a small wire may be 

 seriously impaired or the wire may even be corroded throughout 

 its thickness. On the other hand, by using aluminium for large 

 switchboard connections and for "bus bars" for internal 

 transmission of heavy currents in power stations, etc., very 

 considerable economy may be effected. The same advantage 

 does not accrue from the use of aluminium for insulated and 

 armoured cables. Owing to the increased diameter of the 

 conductor the amount of the dielectric or of the armouring has 

 to be increased largely and the additional cost of the latter 

 frequently more than neutralises the saving made on the cost 

 of the metal. At existing prices, there seems to be a marked 

 saving in the case of single-core cables of large diameter which 

 are not heavily insulated, whereas with three-core cables or 

 insulated cables for high tension currents, the advantage still 

 rests with copper. Every case, therefore, requires separate 

 consideration. A disadvantage attending the use of aluminium 

 for all the purposes cited above is the difficulty of making 

 joints, a difficulty which we shall see later has played so large 

 a part in retarding the introduction of aluminium for chemical 

 plant and one which is not to be met in the way found effective 

 in the latter case. For electrical purposes, joints in aluminium 

 conductors are usually made by purely mechanical means. 



Aluminium is said to have been used successfully for battery 

 connections in storage battery installations but the fact that 

 in such a case it is in contact with the relatively highly 

 electronegative metal lead in an atmosphere which is always 

 charged with sulphuric acid spray seems to make its use for this 

 purpose particularly inadvisable. 1 



1 Since writing the above, the writer has had an opportunity of carefully 

 inspecting a storage battery room in a large London power-station in which the 

 conductors are almost exclusively made of aluminium rods. These conductors 

 were installed about two years ago and are giving great satisfaction. At first 

 there was some difficulty of the nature indicated in the text of this article but it 

 has been overcome by coating the aluminium with an acid-resisting paint. It is 

 clear that so long as steps are taken to prevent the film of electrolyte which forms 

 over the junction of the two metals from being in electrical contact with both or 

 either of them, galvanic action cannot take place. Vaseline seems to be very 

 effective in this way. 



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