96 THE PRODUCTION AND USE OF HEAT 



in a 'smoky atmosphere are liable to injury to their health. 

 Moreover, the smoke and its accompanying dirt have a 

 depressing effect on people. They are liable to become de- 

 spondent and unhappy. This in turn may affect their health. 

 Smoke makes necessary the more frequent painting of build- 

 ings. Stone buildings become dingy and the owners are 

 sometimes put to the expense of washing the entire outside 

 of the building. White clothing becomes soiled because of 

 soot. Furnishings and draperies in houses are injured. 

 Goods on the dealer's shelves are injured because of soot. 

 Our waste due to poor combustion of soft coal runs into 

 millions of dollars annually. 



111. How Can This Waste be Prevented? Of course, the 

 prevention is by practising more perfect combustion of soft 

 coal. Did you ever follow the changes that take place when 

 fresh soft coal is thrown into a stove containing a bed of hot 

 coals? When the coal first meets the hot bed of coals the 

 volatile matter of the coal begins to distill off. If the tem- 

 perature in the stove is fairly high, this volatile matter may 

 undergo more or less complete decomposition into carbon 

 and hydrogen. The hydrogen burns if the oxygen supply 

 is somewhat limited, while the carbon, which requires a 

 greater concentration of oxygen, is burned incompletely or 

 not at all. Black smoke results. If the temperature in the 

 stove is rather low, the volatile matter may not be decom- 

 posed so much. A bluish-gray smoke results. At all events 

 the drafts of the stove are generally not able to supply enough 

 oxygen and maintain at the same time a temperature high 

 enough to burn the volatile matter immediately after throwing 

 fresh coal into the fire. Consequently smoke issues from the 

 chimney as long as there is much volatile matter being produced 

 from the coal. After the volatile matter has been set free, 

 smoke ceases to escape from the chimney until a fresh charge 

 of coal is thrown into the stove. If smaller amounts of coal 

 could be thrown in at shorter intervals of time, it might be that 

 the drafts of the stove would be able to supply enough oxygen 



