MATERIALS PRODUCING HEAT AND LIGHT 237 



in a glass bottle which is held in place by a metallic 

 device which permits the acid to flow out when the ex- 

 tinguisher is overturned. The arrangement of these 



FIG. 77. Working parts of Fire Extinguisher. 



1. Position of acid bottle and decomposing cup C when the Underwriters 

 Extinguisher is not in action. A, cage for acid bottle. B, movable support for 

 opening cage. C, acid decomposing cup acting as bottle closure. D, upper pro- 

 jection or guide stem, operating in socket F. E, lower projection or guide stem, 

 operating in the neck of the acid bottle. F, socket for upper guide stem D. 

 G, sulphuric acid, correct charge bottle half-full. (The two guide stems D and 

 E center and hold the decomposing cup C in its true position at the mouth of 

 the acid bottle, either while the extinguisher is at rest or in action, or in starting 

 and stopping it.) 



2. Position of acid bottle and decomposing cup C, when the extinguisher 

 is in action. H, decomposing cup C filled with acid, showing point where the 

 chemicals come together, when the extinguisher is inverted. (It is at this point 

 that the soda solution attacks and eats the acid out of the decomposing cup, and as 

 decomposition takes place, a fresh supply of acid is fed from the bottle into the 

 cup as fast as needed -but no faster insuring uniform chemical action.) 



3. Shows the depth and interior of the porcelain acid decomposing cup C. 



materials inside the container is shown In Fig. 77. The 

 reaction between the sulphuric acid and bicarbonate of 

 soda rapidly generates carbon dioxide, which furnishes 

 pressure, causing a mixture of the solution and gas to be 



