420 Scientific Intelligence. 



Upon the lecture-table stood a liter flask full of liquid oxygen. 

 On filling a test-tube with it, it appeared milky, but became clear 

 on passing it through filter paper. The image of the liquid 

 thrown on a screen, appeared of a pale blue color. The liquid in 

 the tube boiled violently at the temperature of the air, with a 

 hissing noise, giving off" a white smoke due to the frozen- mois- 

 ture of the surrounding air. Its boiling point, determined 

 thermo-electrically, is —180°. Liquid oxygen is a non-conductor 

 of electricity. Moreover, a spark 0'l mm will not pass through it 

 from a coil giving a long spark in air ; so that it is also a good 

 insulator. Interposed in the path of a beam of light, its absorp- 

 tion spectrum showed clearly the lines A and B of the solar spec- 

 trum, which lines as is well known, are due to absorption by the 

 oxygen in our atmosphere. On accelerating the evaporation of 

 some liquid oxygen by reducing the pressure upon it, Dewar 

 liquefied air in an open test-tube under atmospheric pressure. 

 The liquid air was clearer and fumed less than liquid oxygen. 

 It also boiled more quietly. Common air liquefies at a much 

 lower temperature than oxygen, both gases being liquefied to- 

 gether. In evaporating however, the nitrogen boils off before 

 the oxygen. Placing two or three ounces of liquid air in a test- 

 tube, a smoldering splinter of wood, placed in the upper portion, 

 was not at first ignited. But after the nitrogen had for the most 

 part boiled off, which took nearly five minutes, the wood when 

 immersed burst into flame. He then poured out a wineglassful of 

 liquid air and presented it to Lord Kelvin, who was in the chair. 

 The magnetic properties of liquid oxygen were shown by placing 

 some of it in a cup made of rock salt (in which it assumes the 

 spheroidal state) and putting the cup beneath the poles of a power- 

 ful electromagnet. On completing the circuit, the liquid oxygen 

 rose from the cup and attached itself to the poles, thus connect- 

 ing them together. There it boiled gradually away, sometimes 

 more on one pole than on the other, falling back into the cup 

 when the circuit was opened. With a single pole the oxygen was 

 drawn up out of a tube. Compared with iron, liquid oxygen is 

 about one thousandth as magnetic. Liquid air also goes to the 

 poles of a magnet, there being no separation of the oxygen and 

 nitrogen. It has the same high insulating power as liquid oxygen. 

 Although phosphorus is not attacked on being dropped into 

 liquid oxygen, yet a photographic plate immersed in liquid oxy- 

 gen at —200° was found to be sensitive to light. Dewar gives 

 the following boiling points under atmospheric pressure : carbon 

 dioxide —80°, nitrogen monoxide —90°, ethylene —103°, oxygen 

 — 184°, nitrogen — 198-]°, air —192-2°, carbon monoxide —193°, 

 nitrogen dioxide —153°, marsh gas —164°. Under only 5 to 

 10 mm pressure the boiling points are for CO„ —116°, N 2 —125°, 

 CJI 4 -142°, O -211°, N -225° (solid), air -207° (solid), CO 

 -211°, N 9 O s -176°, CH 4 -201° (solid),— Engineer, lxxiii, 516, 

 June, 1892. G. F. b. 



