HEAT IN RELATION TO THE HUMAN BODY 17 



formula H 2 O whether it is a liquid, or a solid such as ice 

 and snow and frost, or the invisible vapor present at all 

 times in the air about us. The relative weights of oxygen 

 and hydrogen in it remain unchanged. 



When coal burns with a limited supply of oxygen a poi- 

 sonous gas called carbon monoxide (CO) forms. In the pres- 

 ence of more oxygen this gas burns with a bluish flame form- 

 ing carbon dioxide. This flame is often seen above a coal 

 fire. The illuminating gas furnished in towns and cities for 

 fuel and lights contains more or less carbon monoxide, and 

 any leakage of gas from burners or from stoves is dangerous 

 because of its poisonous effects as well as its explosive na- 

 ture when mixed with air. 



Oxidation may go on very slowly wherever uncombined oxy- 

 gen comes in contact with substances with which oxygen 

 unites readily. This slow combustion occurs within water, 

 and it goes on in the cells of the body. The heat liberated in 

 the various tissues ordinarily maintains a temperature of 

 the human body above that of the surrounding atmos- 

 phere. In some animals like the turtle and the snake this 

 oxidation is so slow that they always feel cold when handled 

 because their body temperature is less than that of human 

 beings. 



In the rusting of such metals as iron, oxidation takes place 

 very slowly; in the explosive mixture of gasoline vapor or of 

 illuminating gas with air, it may be instant and violent. 

 Many of the high explosives used in blasting have in their 

 composition sufficient oxygen to make it possible for combus- 

 tion to occur away from the air. 



The temperature to which bodies like kerosene, wood, and 

 coal must be brought in order that combustion may occur is 

 called the kindling temperature, or point of ignition. 



A flame is a burning gas or vapor. A candle flame ceases 

 to exist at its outer surface where combustion is complete. 



