HEATING BUILDINGS 



109 



by taking a large box and putting into it about 6 inches 

 of hay or sawdust or cork shavings and on top of this 

 material setting another box of wood or paper of such a 

 size that a space of about 6 inches will be left between 

 the sides of the two boxes and also about 4 inches from the 

 top of the inside box to the top of the outside box. The 

 space between the two boxes should be filled with the 

 same kind of packing material that was used in the 

 bottom. The lid should fit the top of the large box and 

 be about 4 inches thick with packing material between the 

 upper and lower surfaces of the lid. When the vessel of 

 boiling hot food is placed in 

 the box and the lid closed, 

 the heat cannot escape; the 

 food to be cooked is thus 

 kept at almost the same 

 temperature as when it was 

 placed in the fireless cooker. 

 Hence, the food will cook the 

 same as if left on the fire, 

 but a little more slowly, be- 

 cause a small amount of heat 

 will escape from the food 

 to warm the inside of the 

 fireless cooker. 



The two walls of the fireless cooker, with the packing 

 of sawdust or cork shavings between, enclose a great 

 amount of air in the little spaces between the packing. 

 Air, being a gas, is a very poor conductor of heat, and the 

 packing prevents convection currents from being formed, 

 and so the heat cannot pass from the inside of the cooker 

 to the outside; thus the material is kept at the same 

 temperature as when it was placed in the cooker. 





FIRELESS COOKER 



Made of two boxes and cork 



packing. 



