156 Domestic Science 



below 0. If we assume Charles's Law, the volume at 

 - 1 will be 272 c.c., that at - 10 will be 263 c.c., 

 that at 100 will be 173 c.c., and so on. It is easy to 

 see that continued application of this reasoning will give 

 as the volume at 273. Long before this tempera- 

 ture is reached, most gases become liquids, and we 

 know of no substance, however difficult it be to liquefy, 

 that remains in the gaseous state below 268. Liquids 

 do not obey Charles's Law so that the decrease of the 

 volume of a substance to nothing' is, as might be 

 surmised, impracticable. This temperature, 273, is 

 of importance, however, since it is taken as the zero 

 of a scale of temperature called the " Absolute " scale. 

 The degrees on this scale are of the same value as 

 those on the Centigrade scale, and Absolute temperature 

 may be expressed on the Centigrade scale by subtracting 

 273, while the reverse operation must be performed 

 to change Centigrade temperatures into Absolute. 

 Thus 365 Abs. = 365 - 273 = 92 C. 5 and - 24 C. 

 = _ 24 + 273 = 249 Abs. 



By the utilisation of the Absolute scale of tempera- 

 ture, Charles's Law may be expressed in a very simple 

 form. Thus : 



The volume of a given mass of gas is directly pro- 

 portional to its Absolute temperature. 



100. We will conclude this chapter by describing 

 a method of solving problems in which changes of 

 volume of a gas, caused by changes of both pressure 

 and temperature, are involved. 



A balloon with a capacity of 50,000 cu. ft. is 

 filled with coal-gas at a temperature of 18 and under 

 the atmospheric pressure of 765 mm. How many cu. ft. 

 of gas will have escaped by the time it has risen to an 



