142 NEW RESEARCHES ON LIQUID AIR. 



where the jet impinges on the wall of the vacuum tube, along with a 

 considerable amount of solid. If oxygen gas escapes from the small 

 hole at the pressure of 100 atmospheres, having been cooled previously 

 to — 79° in the vessel 0, a liquid jet is just visible. It is interesting 

 to note, in passing, that Pictet could get no liquid oxygen jet below 

 270 atmospheres. This was due to his stopcock being massive and 

 outside the refrigerator. If the oxygen is replaced by air, no liquid 

 jet can be seen until the pressure is 180 atmospheres, but on raising 

 the pressure to 300 atmospheres the liquid air collected well from the 

 simple nozzle. If the carbon dioxide is cooled by exhaustion (to about 

 1-inch pressure) or — 115°, then liquid air can easily be collected in the 

 small vacuum vessel D, or if the air pressure is raised above 200 atmos- 

 pheres, keeping the cooling at — 79° as before. 1 The chief difficulty is 

 in collecting the liquid, owing to the rapid current of gas. The amount 

 of liquid in the gas jet is small, and its collection is greatly facilitated 

 by directing the spray on a part of the metallic tube above the little 

 hole, or by increasing the resistance to the escaping gas by placing 

 some few turns of the tube, like B in the figure, in the upper portion of 

 the vacuum tube, or generally by pushing in more tube in any form. 

 A vacuum vessel shaped like an egg-glass also works well. This prac- 

 tically economizes the cool gas, which is escaping to reduce the tempera- 

 ture of the gas before expansion, or, in other words, it is the cold 

 regenerative principle. Coleman pointed out long ago that his air 

 machine could be adapted to deliver air at as low a temperature as has 

 yet been produced in physical research. Both Solvay and Linde have 

 taken patents for the production of liquid air by the application of cold 

 regeneration, but the latter has the credit of having succeeded in 

 constructing an industrial apparatus that is lowered in temperature to 

 — 40°, or to the critical point of air, in about fifteen hours, and from 

 which liquid air containing 70 per cent oxygen is collected after that 

 time. 



For better isolation, the pipe can be rolled between two vacuum 

 tubes, the outer one being about 9 inches long and l^inch diameter, as 

 shown in fig. 3, Plate V. The aperture in the metal pipe has a little 

 piece of glass tube over it, which helps the collection of the liquid. 

 With such a simple apparatus, and an air supply at 200 atmospheres 

 with no previous cooling, liquid air begins to collect in about five min- 

 utes, but the liquid jet can be seen in between two and three minutes. 

 It is not advisable to work below 100 atmospheres. 



In fig. 4, Plate V, the metallic tube in the vacuum vessel is placed 

 in horizontal rings, leaving a central tube to allow the glass tube C to 

 pass, which is used to cool bodies or examine gases under compression. 

 The inner tube can be filled for an inch with liquid air under a pressure 



1 The liquefaction is taking place in this condition at li times the critical tempera- 

 ature. Hydrogen similarly expanded at the melting point of air ( — 214° C.) behaves 

 exactly in the same way. 



