Page:Popular Science Monthly Volume 89.djvu/932

 �Driving a nail with a hammer made of mer- cury frozen solid by immersion in liquid air

��918 Popular Mence Monthly

How Expansion Cools ^<:^^^^^^ liquid

It was found that if the com pressed gas was allowed expand through a sma opening its temperature was still further lowerei

Working with these facts in mind, Lindc and Hampson per- fected a process by which they were able not only to obtain far lower tempera- tures than with the old evaporative method, but to lique- fy gases that had hitherto resisted all efforts. The appara- tus used consists of a coil of pipe (see diagram) through which the com- I>ressed gas is per- mitted to pass and expand through a small opening at the

end. First, the air is brought to a pressure of 200 atmospheres by means of the com- pressor. It is discharged from this through the valve N and into the water-cooled jacket C where the heat of compression is abstracted. From there it tiows through ttic smaller coiled pij^c which is concentric- ally arranged within the larger one. As the air reaches the expansion valve H, and flows into the heat-insulated chamber E, its temperature is greatly lowered. The roolcd air then rushes hack through the larger jiipe and lowers the temperature of the succeeding air coming through the smaller pipe. It will be seen, then, that the air emanating at H will gradually become colder until a liquitl state is reached.

Dr. Hampson's a])- I)aratus for the lique- faction of gaseous matter was designed with such ingenuity and constructed so perfectly that com- pressed air at ordi- niry temperatures

passed through the Diagram explaining the apparatus used in

coil came out as a the Linde process for the liquefaction of gases

��at the nozzle in ap- )ximatel>' six minutes. When attempts were made to liciuef\- hxdrogen by this means, it was found that nstead of being coded b\- expansion its tem- perature was actually raised. Later it was discovered that hy- drogen obeyed this law only when its substance was first cooled by contact with some refrigerat- ing medium. In the apparatus enipkned to-da>- for the lique- faction of hydrogen, the gas is first re- duced to a low tem- perature by means of solid carbonic acid and liquid air. By this means, Dewar also brought helium to a liquid state.

��AIR SUPPLY

��COnPRLSSOR

��Gases That Look Like Water

The fact that these liquid gases cannot be kept in ordinary- containers should be readih' appreciated b>- the reader when it is understood how rapidly the>- abstract heat from their surroundings. If liquid air is poured into an ordinary- glass \-esse! it immediately starts to boil and will reduce the container to bits. It must be remembered that liquid air has a boiling point about 180" Centigrade below zero. If litiuid gases, then, are to be kept an\- length of time they must in some way be insulated from the heat of their surround- ings. It has been known for a long time that nothing but tan- gible matter will con- duct heat wa\es. De- war ingeniously took ad\anlage of this fact in a melhotl l)y means of whicii he can pre- ser\e liquid gases o\er a considerable period of time. Ho uses a glass vessel with two walls between which a high \acinmi pre- \ails. If a small

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