Impurity fownd in Nitrogen Gas derived from Urea. 95 



" On the Character of the Impurity found in Nitrogen Gas derived 

 from Urea." By LORD KAYLEIGH, F.E.S. Received August 

 17, 1898. 



It has already* been recorded that nitrogen prepared from urea by 

 the action of sodium hypobromite or hypochlorite, is contaminated 

 with an impurity heavier than nitrogen. The weight of pure nitrogen 

 in the globe employed being 2 '2 99 grams, the gas obtained with hypo- 

 chlorite was 36 milligrams, or about 1 J per cent., heavier. " A test 

 with alkaline pyrogallate appeared to prove the absence from this 

 gas of free oxygen, and only a trace of carbon could be detected when 

 a considerable quantity of the gas was passed over red-hot cupric 

 oxide into solution of baryta." Most gases heavier than nitrogen 

 are excluded from consideration by the thorough treatment with 

 alkali to which the material in question is subjected. In view of the 

 large amount of the impurity, and of the fact that it was removed by 

 passage over red-hot iron, I inclined to identify it with nitrous oxide ; 

 but it appeared that there were strong chemical objections to this 

 explanation, and so the matter was left open at that time. This 

 summer I have returned to it ; and although it is difficult to establish 

 by direct evidence the presence of nitrous oxide, I think there can 

 remain little doubt that this is the true explanation of the anomaly. 

 I need scarcely say that there is here no question of argon beyond the 

 minute traces that might be dissolved in the liquids employed. 



In the present experiments hypochlorite has been employed, and the 

 procedure has been the same as before. The generating bottle, pre- 

 viously exhausted, is first charged with the full quantity of hypochlorite 

 solution, and the urea is subsequently fed in by degrees. The gas 

 passes in succession over cold copper turnings, solid caustic soda, and 

 phosphoric anhydride. In various experiments the excess of weight 

 was found to be variable, from 23 to 36 milligrams. In order to 

 identify the impurity it was desirable to have as much of it as possible, 

 and experiments were undertaken to find out the conditions of maxi- 

 mum weight. A change of procedure to one in which the urea was 

 first introduced, so that the hypochlorite would always be on the point 

 of exhaustion, led in the wrong direction, giving an excess of but 

 7 milligrams. Determinations of refractivity by the apparatus,! which 

 uses only 12 c.c. of gas, allowed the substitution of a miniature 

 generating vessel, and showed that the refractivity (and along with it 

 the density) was increased by a previous heating of the hypochlorite to 

 about 140 C. Acting upon this information, arrangements were made 



* Kayleigli and Kamsay, 'Phil. Trans.,' A (1895), p. 188. 



f 'Koy. Soc. Proc.,' vol. 59, p. 201, 1896; vol. 60, p. 56, 1896. See also 

 Appendix. 



