TEMPERA TURE. 315 



thermometer does not indi^te that boiling water has 100 

 times as much heat as water at 1 C. 



(a.) Temperature, when reckoned from the absolute zero, is called 

 absolute temperature. Absolute temperatures are obtained by add- 

 ing 460 to the reading of a Fahrenheit thermometer, or 273 to the 

 reading of a centigrade thermometer. 



494. Temperature, Volume and Pressure. 



By raising a gas from C. to 273 C., its volume will be 

 doubled. To reduce the gas at this temperature to its 

 original volume, the original pressure must be doubled. 

 From our knowledge of pneumatics and gaseous expansion, 

 we are able to solve certain problems relating to the volume 

 of gases under different pressures and temperatures. 



Examples. (1.) A mass of air at C. and under an atmos- 

 pheric pressure of 30 inches, measures 100 cu. inches ; what will be 

 its volume at 40 C. under a pressure of 28 inches ? First, suppose 

 the pressure to change from 30 inches to 28 inches. The air will 

 expand, the two volumes being in the ratio of 28 to 30 ( 284). In 

 other words, the volume will be f f times 100 cubic inches or 107 \ 

 cu. in. Next, suppose the temperature to change from C. to 

 40 C. The expansion will be -gfo of the volume at C. ; the volume 

 will be 1 \3 of the volume at C. 1/ T times 107| cubic inches 

 =122 |ff inches. Ans. 



The problem may be worked by proportion as follows : 

 28 : 30 



OQ . QA 



01 ; 273 + 40 



(2.) At 150 C., what will be the volume of a gas that measures 

 10 cu. cm. at 15 C. ? 



273 + 15 : 273 + 150 : : 10 : x, .'. x = 14.69 cu. cm. 



(3.) If 100 cu. cm. of hydrogen be measured at 100 C. , what will 

 be the volume of the gas at 100 C.? 



273 + 100 : 273 - 100 : : 100 : a-. .'. x = 40.37 cu. cm. 



