Applied Science 817 



dently great fields still to conquer in the realm of electric 

 illumination. 



Electric Heating 



For heating purposes electricity is much more efficient, since 

 electrical energy is only too willing to change into heat. One of 

 the difficulties associated with large electrical apparatus is that 

 of keeping parts cool enough to prevent insulation being burned 

 away. Domestic electrical heating appliances derive their heat 

 from wires or very thin films of metal or other suitable material 

 through which current is passed in sufficient strength to make 

 them glow. Some electric radiators are practically the same as 

 incandescent lamps in design and construction; others, again, are 

 mere wires wound on refractory material, and exposed to the air. 

 Electric irons, hot-plates, kettles, etc., have the conductor em- 

 bedded in mica or asbestos, in close contact to a metal cover, 

 through which the heat is conducted to the matter to be heated. 

 There are very few cooking or heating operations that cannot 

 be performed electrically. So that we now have, besides electric 

 ovens and hot-plates, electrically heated soldering apparatus, 

 glue-pots, foot-warmers, cigar-lighters, bed-quilts, and so on. 

 The aeroplane pilot, soaring many thousands of feet above 

 the earth, would often be paralysed by the intense cold but for 

 the meshwork of insulated wires hidden in his gloves and 

 other clothing, which distributes a grateful warmth due, when 

 traced back to its source, to a small propeller driving a 

 dynamo. 



Only a comparatively small part of the electrical energy 

 that is purposely converted into heat is used for domestic pur- 

 poses, however. Vast quantities of electrical power are now 

 generated for heating furnaces in which are produced all the 

 aluminium we use, all the calcium carbide from which acetylene 

 gas is made, all artificial abrasives, and certain fertilisers contain- 

 ing nitrogen stolen from the atmosphere. Electrical furnaces 



