1894.] Determinations of the Density of Nitrogen Gas. 341 



dependency of the fact that the action of the copper in the first case 

 was pushed to great lengths, there are two arguments which appeared 

 to exclude the supposition that oxygen was still present in the pre- 

 pared gas. One of these depends upon the large quantity of oxygen 

 that would be required in view of the small difference between the 

 weights of the two gases. As much as l/30th part of oxygen would 

 be necessary to raise the density by 1/200, or about one sixth of all 

 the oxygen originally present. This seemed to be out of the question. 

 But even if so high a degree of imperfection in the action of the 

 copper could be admitted, the large alteration caused by the sub- 

 stitution of oxygen for air in Lupton's process would remain un- 

 explained. Moreover, as has been described in the former paper, the 

 introduction of hydrogen into the gas made no difference, such 

 hydrogen being removed by the hot oxide of copper subsequently 

 traversed. It is surely impossible that the supposed residual oxygen 

 could have survived such treatment. 



Another argument may be founded upon more recent results, 

 presently to be given, from which it appears that almost exactly the 

 same density is found when the oxygen of air is removed by hot iron 

 reduced with hydrogen, instead of by copper, or in the cold by ferrous 

 hydrate. 



But the difficulties in the way of accepting the second alternative 

 are hardly less formidable. For the question at once arises, of what 

 gas, lighter than nitrogen, does the contamination consist ? In order 

 that the reader may the better judge, it may be well to specify more 

 fully what were the arrangements adopted. The gas, whether air or 

 oxygen, after passing through potash was charged with ammonia as 

 it traversed a small wash-bottle, and thence proceeded to the furnace. 

 The first passage through the furnace was in a tube packed with 

 metallic copper, in the form of fine wire. Then followed a wash-bottle 

 sulphuric acid by which the greater part of the excess of am- 

 would be arrested, and a second passage through the furnace 

 a tube containing copper oxide. The gas then traversed a long 

 length of pumice charged with sulphuric acid, and a small wash- 

 bottle containing Nessler solution. On the other side of the regulat- 

 ing tap the arrangements were always as formerly described, and 

 included tubes of finely divided potash and of phosphoric anhydride. 

 The rate of passage was usually about half a litre per hour. 



Of the possible impurities, lighter than nitrogen, those most de- 

 manding consideration are hydrogen, ammonia, and water vapour. 

 The last may be dismissed at once, and the absence of ammonia is 

 almost equally certain. The question of hydrogen appears the most 

 important. But this gas, and hydrocarbons, such as CH 4 , could they 

 be present, should be burnt by the copper oxide ; and the experiments 

 already referred to, in which hydrogen was purposely introduced 



2 B 2 



