92 



THE SUN'S GIFT OF HEAT 



FIGURE 46. DIAGRAM OF A 

 FIRELESS COOKER 



food remains at nearly the boiling point for hours, and is 

 thus cooked. In most cookers, heated pieces of soap- 



J . __ stone are placed above and 



below the dish containing the 

 food. Soapstone has a large 

 capacity for heat. (Page 84.) 

 The fireless cooker can also 

 be used as a refrigerator if 

 the food is cooled before being 

 placed in it or if ice is placed 

 in it with the food. When 

 the cooker is used as a refrigerator, the insulated walls are 

 very slow to conduct the heat of the atmosphere to the 

 cold food, just as they were slow to con- 

 duct the inside heat to the cooler sur- 

 rounding atmosphere. The non-conducting 

 character of the walls protects either way. 

 For that reason the walls of a fireless 

 cooker are similar to those of a refrigerator. 

 Snow on the ground in winter prevents 

 the heat from leaving the ground and the 

 ground from being deeply frozen, just as 

 the sawdust and other materials in the 

 walls of the cooker prevent the heat from 

 being conducted rapidly away from the 

 cooker. That is one reason why farmers 

 like a snowy winter. 



The thermos bottle (Figure 47) is similar 

 to the fireless cooker in principle. It 

 consists of two glass bottles, one placed 

 inside the other, sealed together at the neck. Before the 

 bottles are sealed together the air between them is re- 



FIGURE 47. DIA- 

 GRAM OF A THER- 

 MOS BOTTLE 



