86 JUNIOR GRADE SCIENCE 



the quantity of gas under consideration is measured under the con- 

 ditions existing at the time, and by calrulatioii the volume is found 

 which it would occupy at standard conditions of temperature and 

 pressure. For example, the volume of a quantity of a gas measured 

 when the temperature is 15 C. and the barometer reads 750 mm. at 

 normal temperature and pressure would be calculated as follows : 



(273 + 15) c.c. would become 273 c.c. at 0C. and 7."><> nun. ; 



. . 1 c.c. m c.c. at C. and 750 nun., 



and (section 27) 1 c.c. f $ x f $g c.c, at C. and 760 mm. 



In a similar manner the volume of any quantity of gas under Normal, 

 or Standard, conditions of Temperature and Pressure (N.T.P.) can le 



found. 



Coefficient of expansion of gases. 



Volume at 

 ,-tant Pressiin-. 

 Hydrogen, ...... 0-00366 



Air, - - 0-00367 



Carbon dioxide, ..... <MMW7I 



QUESTIONS ON CHAPTERS XIII.- XV. 



66. Bodies in general expand when heated. From every-day life give 

 three typical examples of this fact and state one remarkable exception. 



67. In what respects does a gas differ from a liquid ? Describe how you 

 would show the points of difference. 



68. How would you investigate the effect of increase of temperature on 

 the volume of a quantity of water ? 



69. How is a Centigrade thermometer constructed and graduated ? 

 When the temperature of a room in 15 on a Centigrade thermometer, what 



would be the reading of a Fahrenheit thermometer ? Explain your method 

 of calculation. 



70. Having filled a thermometer, how would you proceed to graduate 

 it so as to enable you to use it for measuring temperatures ? 



71. Define the coefficient of expansion of air, and describe how you would 

 find its value. 



72. How would you determine the coefficient of expansion of air ? 



A vessel contains 500 c.c. of air at C. and a pressure of 77 cm. of mercury. 



First, the air is allowed to expand until the pressure is 70 cm., no change 

 of temperature occurring during this expansion, and then the temperature 

 is raised to 30 C., the gas being now allowed to expand in such a way that 

 no further change of pressure takes place. What is the final volume ? 

 (The coefficient of expansion 



