Producing^^the Coldest Cold 



Think of 400 de- 

 grees below zero ! 



Burning a piece of cold-rolled steel in liquid an . The liquefied oxygen 

 combines so rapidly with the metal that a furious heat is produced 



At right: By using a vacuum 

 pump the rate of evaporation can be 

 increased enough to freeze the air 

 contacting the outside of the tube 



AMONCi the more start- 

 AA Hng discoveries of the 

 jjast decade is the pro- 

 duction of temperatures reach- 

 ing as far as 400° F. below- 

 zero. It is the attainment of 

 these low temperatures that 

 has brought the chemist and 

 plu'sicist into a new world; 

 for when matter is subjected 

 to such degrees of cold, there 

 is a complete alteralinii of 

 both its chemical and jilusical 

 jjropcrtics. 



Each substance on our 

 earth has individual properties, Ixitli ( luin- 

 ical and physical, whicli it can retain onl\' 

 at a specific temperature — a temperature 



916 



Think of gases that have been squeezed 

 and cooled until they look like water! 



which nature set for it. 

 If we alter this tempera- 

 ture by artificial means the 

 substance will gradualh- 

 assume a difl'erent physical 

 state. This change of state 

 is "forced" upon it, and 

 when we withdraw the arti- 

 ficial means of changing its 

 temperature, nature 

 promptly transforms tl.c 

 substance into its origincl 

 state. As an example, 

 water at ordinary tempera- 

 ture is a liquid. If we heat 

 it to 212° F. it becomes 

 steam, and if we cool it to 

 32° 1". it becomes a solid. 

 What is known as the 

 kinetic theory of matter 

 tells us that all molecules 

 are in perpetual \ibr£:licn 

 at a tremendous \cIocity 

 and are continually collid- 

 ing with one another. This 

 rate of molecular \ibration 

 produces the temperature 

 of matter — the higher the 

 rate of motion the greater 

 the temperature and vice 

 versa. The molecules are in- 

 cessanth' gi\ing out their 

 energy of motion and at the 

 same time are recei\ing these 

 meclianical impulses from 

 otlicr ]iarticles of matter. 

 With these simple facts i:i 

 mind, we may continue more 

 intelligently. 



W'lien we boil water 

 we merely impart ener- 

 gy in the form of heat 

 to the molecules. If 

 the source of heat is intense 

 enough, the particles become 

 I so wild in their vibration that 

 the>' come out of the range of 

 their natural nnitual attrac- 

 tion and pass olT as vapor. If 

 this vapor is cooled it again 

 assiunes the liquid state, be- 

 cause we ha\e taken energy 



