106 Domestic Science 



Boyle's Law. The substances which show this peculi- 

 arity are all obtainable in the liquid form at ordinary 

 temperatures by being sufficiently compressed and, on 

 cooling them to temperatures which are not far removed 

 from the ordinary temperature, also assume the liquid 

 form. Sulphur dioxide a gas obtained by burning 

 sulphur in air is an example of this class. It becomes 

 a liquid at 10 C. under atmospheric pressure, and 

 is obtainable commercially in the liquid form, being 

 stored in stout bottles resembling soda-water syphons. 

 It is forced into these bottles under pressure and is 

 retained in them as a liquid at all ordinary tempera- 

 tures. Such a gas readily liquefiable by cold, and 

 capable of liquefaction at ordinary temperatures by 

 pressure alone is frequently termed a "vapour". On 

 the other hand, nitrogen one of the gases of the 

 atmosphere must be cooled to - 195 C. under 

 atmospheric pressure before becoming a liquid, and 

 cannot be liquefied by increase of pressure alone at 

 ordinary temperatures. At temperatures near its 

 boiling-point, however, nitrogen exists in the vaporous 

 condition, being then readily liquefiable by increase of 

 pressure alone. 



65. Problems dealing with the changes of volume 

 of gases with change of pressure may be readily solved 

 by such methods as that shown in the following 

 example : 



A room is 15 ft. long, 12 ft. wide, and 8 ft. 6 in. 

 high. Find the volume of air which escapes from 

 the room when the atmospheric pressure alters from 

 750 mm. to 735 mm. 



The interior volume of the room, and hence that of 

 the air contained in it, is (15 x 12 x 8|) = 1530 cu. ft. 

 The product of the numbers representing the volume 



