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 tlie 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 



