Impurity found in Nitrogen Gas derived from Urea. 97 



little oxygen, the recognition of which would lead to a rise in the 

 second value of #, and a fall in the first. Examination of the gas 

 from the refractometer with alkaline pyrogallate proved that oxygen 

 was actually present. 



Evidence may also be obtained by exploding the gas with excess of 

 hydrogen, for which purpose oxy-hydrogen gas must be added. But 

 when nitrous oxide is in question, operations over water are useless, 

 while for the more exact procedure with mercury, experience and 

 appliances were somewhat deficient. The contraction observed was 

 rather in excess of the volume of nitrous oxide supposed to be present, 

 but of this a good part is readily explained by a small proportion of 

 free oxygen. 



If the impurity is really nitrous oxide, it should admit of concentra- 

 tion by solution in water. To test this, about 1 litre of water (cooled 

 with ice) was shaken with the contents of a globe (about 2 litres). 

 The dissolved gases were then expelled by boiling, and were collected 

 over water rendered alkaline, in order to guard against the introduction 

 of C0 2 . The quantity was, of course, too small for weighing, but it 

 could readily be examined in the refractometer. Of one sample, after 

 desiccation, the refractivity relatively to air was found to be as high 

 as 1-207, although some air was known to have entered accidentally. 

 The proportion of nitrous oxide in a mixture with nitrogen which 

 would have this refractivity is 0*255. The impurity thus agrees with 

 nitrous oxide in being very much more soluble in water than are the 

 gases of the atmosphere. 



In the analytical use of hypobromite for the determination of urea, 

 it has been noticed* that the nitrogen collected is deficient by about 

 8 per cent., but the matter does not appear to have been further 

 examined. The deficiency might be attributed to a part of the urea 

 remaining undecomposed, but more probably to oxidation of nitrogen. 

 In default of analysis any nitrogen collected as nitrous oxide would 

 not appear anomalous, and the explanation suggested requires the 

 formation in addition of higher oxides retained by the alkali. 



There is reason to suspect that nitrogen prepared by the action of 

 chlorine upon ammonia is also contaminated with nitrous oxide, and 

 this is a matter of interest, for the contamination in this case cannot 

 well be referred to a carbon compound. In two trials with distinct 

 samples the refractivities were decidedly in excess of that of pure 

 nitrogen. 



APPENDIX. 

 Details of Refractomcter. 



Determinations of refractivity have proved so useful and can be 

 made so readily and upon such small quantities of gas, that it may be 

 * Russell and West, 'Client, Soc. Journ,,' vol. 12, p. 749, 1874. 



