October 19, 191 1] 



NAT URL 



in the form of a tube of thin tinned copper or a lead 

 alloy pressed round the insulated wire, and forming 

 an integral part of it. When low-voltage wiring is 

 supplied through a double-wound transformer, the outer 

 metal sheathing of the wire is used as a return con- 

 ductor ; in the case of the lead-covered wire there is 

 a thin copper tape under the lead to improve the 

 conductance. For continuous current and houses sup- 

 plied through an auto-transformer, a twin wire is 

 usually employed, the two wires being under one 



sheath. In both 

 cases it is essen- 

 tial that the outer 

 sheath shall be 

 mechanically con- 

 tinuous; in the 

 concentric system 

 this is obvious, 

 and in the twin 

 system the con- 

 tinuity of the 

 casing, which is 

 then earthed at 

 one end, is neces- 

 sary to secure 

 immunity from 

 shock or fire in 

 case of leakage. 

 The necessary 

 "bonding " of the 

 sheathing, there- 

 fore, forms part of 

 Switch (cover the " system," and 

 various simple ar- 

 rangements are 

 used for connecting the wires to the fittings, which 

 effectually prevent this bonding from being omitted. 



In comparison with the triumphs that have been 

 accomplished in the laboratory and works in connec- 

 tion with lamp manufacture, the improvements in 

 heating and cooking apparatus will appear slight. 

 They are largely pure improvements in constructional 

 details. The success of electric cooking has been 



Auxiliary Ct 



almost entirely due to the possibility of bringing the 

 actual heating element in the closest possible 

 proximity to the object to be heated, so as to heat 

 nothing else than the actual surfaces required for the 

 cooking operation ; this is, of course, not possible to 

 such a degree either with coal or gas cooking. To 

 illustrate this two of the simplest examples may be 

 taken. Fig. 3 is a "table toaster" shown open. The 

 heating element is a ribbon of high-resistance alloy 

 wound spirally on strips of mica. This glows with 

 NO. 219O, VOL. 87] 



a dull-red heat when current is turned on. The bread 

 is placed in the removable sides (one only is seen in 

 the illustration), a piece on either side of the heater, 

 and these are closed up so that the bread is held 

 vertically, and parallel to the surface of the heater, 

 with only a very short space between. As a result 

 the bread is toasted absolutely evenly, and with no 

 loss of heat at all. Fig. 4 is a section of the lower 

 part of an electric kettle, and it is seen that the 



Fig. 3.— Electric " Table Toaster." (Simplex Conduits, Ltd.) 



heating element projects into the bottom of the 

 kettle, and is practically surrounded by the water. 



In the larger cooking apparatus similar means are 

 taken to bring the heating elements exactly where they 

 are wanted, and to reduce the amount of heat lost by 

 radiation and convection to a minimum. For instance, 

 in most forms of electric oven at least three of the 

 sides contain heating elements quite close to the in- 

 terior surface ; in nearly all makes the lagging is very 

 thoroughly carried out, while others rely to some 

 extent on giving the outside of the apparatus a bright 

 surface to reduce radiation. It has also been proved 

 by experiment that in roasting a joint in an electric 



oven, owing to the more even distribution of the heat 

 there is less shrinkage of the meat, so that it retains 

 its gravy ; it appears that the smallest possible diminu- 

 tion of weight in a joint during cooking is an object 

 aimed at by cooks and housewives, and that in this 

 respect the electric oven has the same superiority over 

 the gas oven as the gas oven has over the ordinary 

 coal-fired kitchen range. The precision with which 

 the heat can be regulated by switching on or off the 

 heating elements as required is also a great advantage 

 both as regards good cooking and absence of waste, 

 and several makers adopt a series-parallel arrangement 

 of connections and switching, so that all the elements 

 are utilised, whether at full, half, or quarter heat, and 

 there is absolute uniformity of temperature over the 

 whole of the heating surface. 



