138 



Professor Deivar 



[March 27, 



nitrogen and air nitrogen, with its • 1 per cent, of argon, behaved in 

 substantially the same way on liquefaction. 



Liquid Nitric Oxide. — Great interest attaches to the behaviour of 

 nitric oxide at low temperatures. Professor Olszewski has examined 

 the liquid and describes it as colourless. Samples of nitric oxide 

 have been prepared in different ways. These have been transferred 

 to liquefaction flasks, where they were left in contact with anhydrous 

 potash, sulphuric acid alone, a mixture of sulphate of aniline and 

 sulphuric acid, or phosphoric acid, for many days before use. Each 

 of the samples, when cooled, gave a nearly white solid, melting into 

 a blue liquid. The colour is more marked at the melting point than 

 at the boiling point. Liquid nitric oxide is not magnetic ; neither is 

 the solid phosphorescent. Colour in the oxides of nitrogen evidently 

 begins with the second oxide. Solid nitric oxide does not show any 

 chemical action when j^laced in contact with liquid oxygen, provided 

 the tube containing it is completely immersed ; but if the tube full 

 of liquid oxygen is lifted into the air, almost instantly a violent 

 explosion takes place. 



Specific Gravities tahen in Liquid Oxygen. — In a good vacuum 

 vessel specific gravities may be taken in liquid oxygen with as great 

 ease as in water. The shape of the vacuum vessel which works best is 

 shown in Fig. 4. It must contain excess of mercury and be thoroughly 

 boiled out, so that the inner vessel becomes completely coated with a 

 mercury mirror as soon as the liquid oxygen is filled in. Instead of a 

 mercury vacuum, the interior may be silvered and highly exhausted 

 by a Sprengel pump. The flasks must also be thoroughly clean and 

 free from dust, otherwise the liquid oxygen will not remain tranquil. 

 Any superheating is prevented by inserting a long narrow piece of 

 wood for a moment before the final weighing. 



Some twenty substances were weighed in liquid oxygen,* and the 

 apparent relative density of the oxygen determined. The results 

 were then corrected, using Fizeau's values for the variation of the 

 coefficient of expansion of the solids employed, and thereby the 

 real density of liquid oxygen calculated. The resulting value was 

 1'1375, bar. 766-5, in the case of such different substances as 

 cadmium, silver, lead, copper, silver iodide, calc-spar, rock crystal. 

 The following table sives some of the observations : — 



♦ The liquid oxygen might possibly contain a small proportion of nitrogen. 



