CHAPTER VIII 



THE EFFECT ON LIFE OF LESSENING THE 

 BAKOMETEIC PRESSUEE 



ACCORDING to the kinetic theory of gases, the molecules of a gas 

 are in a state of constant motion, and the pressure exerted by a 

 gas on its neighbourhood, whether solid, liquid, or gas, is measured 

 by the number of molecular impacts per unit of time. If the gas 

 within a chamber be compressed, the paths of the atoms are short- 

 ened, the number of impacts increased, and the pressure rises. If 

 the temperature be raised the speed of the movement increases, the 

 number of impacts increase in unit time, and the pressure rises. 

 When a gas is suddenly compressed the rate of impact is increased 

 by the push, and the temperature rises ; conversely, when it is 

 decompressed allowed suddenly to expand the temperature falls. 



When air under constant pressure is heated it expands by 

 0-000367 of its volume at C. for each degree Centigrade. Thus 1 litre 

 of air at 0. becomes 1-00367 1. at 1 C., and 1-0367 1. at 10 C. 

 To find what the observed volume of a gas at the observed tempera- 

 ture t 0. would be when reduced to C. we have 



V : V = 1 : 1 + 0-00367 t 



' V - 



~ 



1 + 0-00367 t 



At a constant temperature the volume of a gas is in inverse 

 proportion to the pressure. A litre of air at one atmosphere occupies 

 half a litre if compressed to two atmospheres. To find what the volume 

 of a gas measured under a pressure p will be under normal pressure 

 760 mm. we have 



760 

 These two formulae can be combined as one 



~ 760(1 + 0-00367) t 



and this is the formula used for reducing all gas volumes to the 

 standard C. and 760 mm. If the gases are measured wet, the 



210 



