26 



HEAT 



The invention of the " Fireless Cooker " depended in part 

 upon the principle of non-conduction. Two vessels, one inside 

 the other, are separated by sawdust, asbestos, or other poor con- 

 ducting material (Fig. 18). Foods are heated in the usual way 

 to the boiling point or to a high temperature, and are then 

 placed in the inner vessel. The heat of the food cannot 



escape through the 

 non-conducting mate- 

 rial which surrounds 

 it, and hence remains 

 in the food and slowly 

 cooks it. 



A very interesting 

 experiment for the 

 testing of the efficacy 

 of non-conductors may 

 be easily performed. 

 Place hot water in a 



metal vessel, and note by means of a thermometer the rapid- 

 ity with which the water cools; then place water of the same 

 temperature in a second metal vessel similar to the first, but 

 surrounded by asbestos or other non-conducting material, 

 and note the slowness with which the temperature falls. 



FIG. 18. A fireless cooker. 



