138 



RELATION OF HEAT TO COMFORT 



and point the glass tubing toward the fire. The gas gener- 

 ated is carbon dioxide. It is heavier than air, does not burn, 

 and does not aid burning. 



What makes the liquid come out of the bottle? What 

 causes the fire to go out? 



READINGS WHICH WILL HELP ANSWER 

 THE PROBLEM QUESTIONS 



We have already learned that fuels contain carbon 

 and hydrogen which unite with oxygen from the air 

 during combustion. Everyone knows from common 

 observation, however, that a piece of paper or a stick 

 of wood will not start burning of itself. Why is this? 



What is meant by kindling temperature? In addition 

 to oxygen, the proper temperature is needed for -burn- 

 ing. The temperature at which a substance starts burning 

 is called its kindling temperature. Different substances 

 require different degrees of intensity of heat to take 

 fire, and some substances have much lower kindling 

 temperatures than others. If you have performed the 

 experiment suggested at the beginning of this topic, 

 you should have noticed that phosphorus started 

 burning much more quickly than paper or wood. This 

 was because its kindling temperature is much lower 

 than that of the other substances. 



When we want to imrn coal we usually put paper 

 in the stove or furnace first, then "kindling" wood on 

 top of the paper. The heat from a match furnishes 

 sufficient heat to ignite the paper, and the heat from 

 the burning paper raises wood to its kindling tempera- 

 ture. After the wood is burning well we put coal on 

 top, as sufficient heat is developed by burning wood 

 to raise coal to its kindling temperature. 



How did our forefathers light their fires? How or 

 when man first learned- to start a fire is not known. It 

 is known that before historic times fires were started 

 by rubbing two pieces of wood together until enough 

 heat was produced to make a spark which was used to 

 kindle a fire (Fig. 22C). Another primitive method 

 consisted of striking flint (a type of rock) upon steel 

 to produce a spark. 



Our forefathers used the flint-and-steel method to 

 start their fires. The sparks produced were caught in 

 some tinder, a substance such as dried bark or moss 

 which caught fire readily. It was a common practice 

 before the invention of matches to save hot coals each 

 evening to start the fire the next day rather than use 

 flint and steel every time a fire was needed. If the 

 coals went out before morning, as they occasionally 

 did, it was the custom to borrow some from a neigh- 

 bor. The hot coals were carried in little covered iron 

 containers made especially for that purpose. 



What are the scientific principles underlying the 

 match? During the seventeenth century it was dis- 

 covered that sulphur could be used in making a fire 

 because it begins to burn at a much lower temperature 



than wood and because the heat furnished is sufficient 

 to ignite wood. The "parlor match" was not invented, 

 however, until about 1823. The head of the common 

 "strike-anywhere" match usually consists of a mix- 

 ture of phosphorus, potassium chlorate (a substance 

 containing oxygen), powdered glass or sand, and 

 glue. Since phosphorus has a very low kindling tem- 



Keystone View Company 



FIG. 220. MAKING FIRE BY FRICTION 



perature, rubbing the match against a rough surface 

 produces enough heat to ignite the phosphorus, which 

 in turn lights the match stick. 



The head of a safety match is made of a substance 

 that burns readily, and the phosphorus and powdered- 

 glass or sand are placed on the rubbing surface of the- 

 box. The head of the match will not burn unless rub^I.^ 

 bed over the phosphorus on the box. 



How may fire be controlled? Fire is of inestimable" 

 value to man, but when it gets out of control it causes - 

 tremendous damage and loss. Records kept by fire in- 

 surance companies and government bureaus show" 

 that the property losses in this country from fire alone 

 amount to over a half billion dollars a year. Also 

 thousands of people lose their lives each year from 

 fire. Most fires are caused by thoughtlessness and 

 carelessness in the care of things about homes and 

 buildings, such as the heating plant and chimney, 

 rubbish, matches, electrical devices and wiring, and 

 the use of kerosene and gasoline. 



The improper care of heating devices frequently re- 

 sults in disastrous fires. Hot stove and heater pipes 



