PROJECTS 585 



correctly, discharge the extinguisher again in a second experiment 

 with a small bonfire. 



One of the machines that generates carbonic acid gas also pro- 

 duces a foam, the bubbles of which imprison the carbonic acid gas 

 and form a sort of foamy blanket that is especially effective in 

 extinguishing burning oils. 



Another very commonly used extinguisher, which is compact 

 enough to be convenient for automobile use, is filled with a liquid 

 that contains carbon tetrachloride. When this liquid comes in 

 contact with heat, it is readily converted into a heavy gas which 

 smothers the fire just as carbon dioxide does. This machine is 

 operated like a simple hand-pump. 



PROJECT XX. How to Make a Fireless Cooker at Home, 

 page 91 



A very satisfactory fireless cooker may be made at home at 

 relatively slight expense. 



The Box or Container. The outside of the box may be a tightly 

 built wooden box, an old trunk, a galvanized iron ash can, a large 

 lard tin or butter firkin. 



A well-built conveniently sized box (Figure 10, A}, with a hinged 

 cover (Figure 10, #), fitted with a hasp lock is perhaps the most 

 satisfactory container, although the cooker incased in metal has 

 the advantage of being fireproof. If a box is to be used, its size 

 will depend on the size of the metal nest which holds the cooking 

 vessel (Figure 10, (7). If possible, the box and the nest should be 

 large enough to accommodate a six-quart cooking vessel (Figure 

 10, D) . There must be enough space in the container to allow for 

 at least four inches of packing material above, below, and all around 

 the metal nest. 



Packing or Insulating Material. For insulating material a 

 variety of substances may be used. Crumpled or shredded news- 

 paper, sawdust, cotton-seed hulls, ground cork (such as is used 

 in packing Malaga grapes), wool, Spanish moss, hay, straw, and 

 excelsior may be used satisfactorily (Figure 10, B). 



