46 



regular contraction continued so far, the sample would, by cal- 

 culation, at least, lose all its volume. This temperature (the 

 lowest temperature that could possibly be attained) is called the 

 absolute zero. In point of fact, however, all gases liquefy before 

 the temperature has fallen to 273. 



The rule contained in these statements is known as Charles' 

 law. By applying an arithmetical device, we can state the law in 

 a form which makes its use in calculations quite easy. The 

 device consists in adding 273 algebraically to all temperatures. The 

 temperature, when 273 has been added, is called the absolute 

 temperature. The rule then reads: The volume of a sample of 

 any gas is directly proportional to the absolute temperature. 



Thus, a sample of gas occupies 45 c.c. at 15, what would be its 

 volume at 10? After we have applied the device, this reads: 

 a sample of gas occupies 45 c.c. at 15 + 273 = 288 Abs., what 

 would be its volume at 10 + 273 = 283 Abs.? The volume 

 changes in the ratio of these absolute temperatures. Since the 

 new temperature (10 C. or 283 Abs.) is lower, the volume be- 

 comes smaller. Therefore, putting the smaller number in the 



900 

 numerator, the volume at 283 = 45 X ~ 5 = 44.2 c.c. 



Joo 



Again, a sample of gas occupies 125 c.c. at 25, what will be its 

 volume at 15? The absolute temperatures are 25 + 273 = 

 298 Abs., and - 15 + 273 = 258 Abs. As the new temper- 

 ature is lower, the volume will be less. Hence the new volume 



OKO 



125 X ? = 108.2 c.c. 



In practice, when a sample of gas is measured, we read the 

 existing temperature, and correct the volume to that which the 

 sample specimen would occupy at C. For example, the 

 volume is 102 c.c. at 18, what is it at 0? The absolute temper- 

 atures are 18 + 273 = 291 Abs., and + 273 = 273 Abs. The 

 new volume will be smaller. Hence, the new volume is 102 X 



