534 Messrs. Owen and Hughes on Condensation Nuclei 



Oxygen was generated by beating a Jena-glass tube con- 

 taining pure potassium permanganate. The gas passed 

 through a long U-tube containing soda-lime, and then through 

 a narrow glass tube 6 feet long bent into a spiral and immersed 

 in liquid air. The oxygen was then condensed in a tube 

 (similar to R in the figure) by surrounding it with liquid air. 

 Enough oxygen was condensed to give about 20 litres of the 

 gas. When this quantity of liquid oxygen was obtained the 

 permanganate tube and spiral were cut off by means o£ a tap. 

 The only piece of rubber used in the whole apparatus was 

 the one connecting the permanganate tube to the tube of 

 soda-lime. 



The general results were almost identical with those obtained 

 for air, the " critical temperature " at a pressure of 101 

 centims. being again about — 140° C. At the lower pressure 

 of 41 centims. the critical temperature seemed somewhat 

 lower than in the case of air ; but on cooling by liquid air at 

 this pressure, the oxygen in the tester liquefied and dense 

 coloured showers or clouds were obtained. 



Nitrogen. 



Experiments were performed on nitrogen prepared in two 

 ways. One method of preparation was to heat gently a 

 mixture of equal parts of ammonium chloride, sodium nitrite, 

 and potassium bichromate. The gas passed through KOH, 

 H 2 S0 4 , CaCl 2 , P2O5, the long spiral immersed in liquid air 

 and a plug of glass-wool. The joints were all of sealed glass. 

 This method is open to the objection that the nitrogen pre- 

 pared in this way may contain traces of oxides of nitrogen. 



The other method adopted was to drop ammonium chloride 

 slowly into a solution of sodium hypobromite. The nitrogen 

 evolved was then passed through sulphuric acid, over hot 

 copper, through wash-bottles containing sulphuric acid, and 

 potash, through calcium chloride and phosphorus pentoxide, 

 the long spiral immersed in liquid air and a plug of cotton- 

 wool. The results for nitrogen are not so consistent as for 

 air and oxygen, probably owing to its being so very difficult 

 to obtain this gas in a pure state. At a pressure of 101 

 centims. the gas had only to be cooled to about —125° C. to 

 cause the nuclei to appear. At the lower pressure of 41 

 centims., however, the "critical temperature" is approxi- 

 mately the same as in the case of air. 



