Page:Popular Science Monthly Volume 89.djvu/930

 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, which it can retain onl\' at a specific temperature — a temperature

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��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

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