Fire and Heat 141 



9. What is the ratio by volume of the gases that compose hydrogen 

 dioxid ? 10. Why should a lantern be lowered into an old well before 

 men go down into it? 11. After an explosion in mines men not 

 injured by ,the explosion may be suffocated by " choke damp." What 

 is "choke damp"? 12. An alcohol lamp does not deposit soot. 

 Describe fully how you would prove that alcohol contains carbon in 

 its composition. 13. In what way may the diamond be proved to 

 be carbon? 14. In what ways did the formation of coal prepare the 

 earth for man's existence? 15. When you see smoke issuing from 

 your chimney, what use can you make of the knowledge of the prod- 

 ucts of combustion in deciding whether or not the furnace is being 

 properly managed? 16. If black smoke appears, what may be 

 wrong in the management of the furnace? 17. Why is the knowledge 

 of what flue gases contain useful to an engineer? 18. Is too much 

 air entering a furnace as wasteful of fuel as too little ? 19. Why is 

 burning a safe method of garbage disposal ? 



VI. MEASURING HEAT 



It is common knowledge that different kinds of coal vary 

 greatly in the way in which they burn and in the amount of 

 heat they produce. S'o it is with all kinds of fuel, such as wood, 

 oil, gas, gasoline, and alcohol. We compare one kind of fuel 

 with another, estimating their heating value by their effect 

 in warming various things. Such an estimate is of course vague 

 and of limited practical value ; but it indicates the possibility 

 of an exact or scientific method of measuring quantities of heat 

 based upon its effect in raising the temperature of objects, such 

 as iron, air, or water. If we have such an exact method of 

 measurement, that is, a unit quantity or measure which will 

 apply to different quantities of heat as a yardstick applies to 

 different dimensions, we can readily apply it to the quantities 

 of heat produced from different fuels and thereby determine 

 their heating values or heat-giving powers. 



53. Heat units. It is not difficult to determine such a unit 

 quantity of heat or unit measure. It involves chiefly the selec- 

 tion of some substance which responds uniformly to heat, 

 showing a definite change in temperature for a definite quantity 



