NEW RESEARCHES ON LIQUID AIR. 147 



nozzle under 140 atmospheres pressure, and yet no liquid jet could be 

 seeu. If the hydrogen contained a few per cent of oxygen the gas jet 

 was visible, and the liquid collected, which was chiefly oxygen, con- 

 tained hydrogen in solution, the gas given oft* for some time being- 

 explosive. 



If, however, hydrogen, cooled by a bath of boiling air, is allowed to 

 expand at 200 atmospheres over a regenerative coil previously cooled to 

 the same temperature and similar in construction to that shown in Plate 

 VII, 1 a liquid jet can be seen after the circulation has continued for a few 

 minutes, along with a liquid which is in rapid rotation in the lower part 

 of the vacuum vessel. The liquid did not accumlate, owing to its low 

 specific gravity and the rapid current of gas. These difficulties will 

 be overcome by the use of a differently shaped vacuum vessel and by 

 better isolation. That liquid hydrogen can be collected and manipu- 

 lated in vacuum vessels of proper construction can not be doubted. 

 The liquid jet can be used in the meantime (until special apparatus is 

 completed for its collection) as a cooling agent — like the spray of liquid 

 Sir obtained under similar circumstances — and this being practicable, 

 the only difficulty is one of expense. In order to test, in the first 

 instauce, what the hydrogen jet could do in the production of lower 

 temperatures, liquid air and oxygen were placed in the lower part of 

 the vacuum tube, just covering the jet. The result was that in a few 

 minutes about 50 c. c. of the respective liquids were transformed into 

 hard, white solids resembling avalanche snow, quite different in appear- 

 ance from the jelly-like mass of solid air got by the use of the air pump. 

 The solid oxygen had a pale, bluish color, showing by reflection all the 

 absorption bands of the liquid. The temperatures reached and other 

 matters will be dealt with in a separate communication. When the 

 hydrogen jet was produced under the surface of liquid air, the upper 

 part of the fluid seemed to become specifically lighter, as a well marked 

 line of separation could be seen traveling downward. This appearance 

 is no doubt due in part to the greater volatility of the nitrogen and the 

 considerable difference in density between liquid oxygen and nitrogen. 

 In a short time solid pieces of air floated about, and the liquid subse- 

 quently falling below the level of the jet, hydrogen now issued into a 

 gaseous atmosphere containing air, which froze solid all round the jet. 

 There is no reason why a spray of liquid hydrogen at its boiling point 

 in an open vacuum vessel should not be used as a cooling agent, in 

 order to study the properties of matter at some 20° or 30° above the 

 absolute zero. 



Fluorine. — This is the only widely distributed element that has not 

 been liquefied. Some years ago Wallach and Hensler pointed out that 

 an examination of the boiling points of substituted halogen organic 



1 In the figure, A represents one of the hydrogen cylindres; B and C, vacuum ves- 

 sels containing carbonic acid under exhaustion and liquid air, respectively; D, 

 regenerating coil; G, pin-hole nozzle; F, valve. 



