158 



NA TURE 



[June 14, 1894 



In both cases a red hot tube containing copper is employed, 

 but with this difference. In the latter method the atmospheric 

 oxygen is removed by oxidation of the copper itself, while in 

 Lupton's method it combines with the hydrogen of ammonia, 

 through which the air is caused to pass on its way to the 

 furnace, the copper remaining unaltered. In order to exag- 

 gerate the effect, the air was subsequently replaced by oxygen. 

 Under these conditions the whole, instead of only about one- 

 seventh part of the niirogen is derived from ammonia, and the 

 discrepancy was found to be exalted to about one half per 

 cent. 



Upon the assumption that similar gas should be obtained by 

 both methods, we may explain the discrepancy by supposing 

 either that the atmospheric nitrogen was too heavy on account 

 of imperfect removal of oxygen, or that the ammonia nitrogen 

 was too light on account of contamination with gases lighter 

 than pure nitrogen. Independently 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 sup- 

 position that oxygen was still present in the prepared 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,'30lh part of oxygen 

 would be necessary to raise the density by i 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 imperfec- 

 tion in the action of the copper could be admitted, the large 

 alteration caused by the substitution of oxygen for air in Lupton's 

 process would remain unexplained. 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 sur- 

 vived 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 difficuliies in the way of accepting the second alter- 

 native are hardly less formidable. For the question at once 

 arises, of what ga;, 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 of 

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

 monia would be arrested, and a second passage through the 

 furnace' in a tube containing copper oxide. The g.is then 

 traversed a long length of pumice charged with sulphuric acid, 

 and a small wash-boule containing Nessler solution. On the 

 other side of the regulating lap 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 halfa litre per hour. 



Of the po-sible impurities lighter than niirogen, those most 

 demanding 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 met important. But this gas, and hydrocarbons, 

 such as CII,. could Ihcy be present, should be burnt by the 

 copper oxide ; and ihe experiments already referred to, in which 

 hydrogen wa; purposely introduced into atmospheric nitrogen, 

 srem to prove conclusively that the burning would really take 

 place. Some further experiments of the same kind will presently 

 be given. 



The gas from ammonia and oxygen wa« sometimes odourless, 

 but at other timcn smelt strongly of nitrous fumes, and, after 

 mixture with moist air, rcdilcncd litmus paper. On one occasion I 

 the oxidation of the nitrogen went so far that the gas showed 

 colour in the blow-off tube of the Tippler, although the thick- 

 ness of the layer was only about half an inch. But the presence 

 of nitric oxide i.<i, ofcourse, no explanation of the abnormal light- 

 neu. The conditions under which the oxidation takes place 

 proved to be difficult of control, and it was thought desirable 

 lo examine nitrogen derived by reduction from nitric and nitrous 

 oxides. 



SO. I2S5, VOL. 50] 



The former source was the firs; experimented upon. The gas 

 was evolved from copper and diluted nitric acid in the usual 

 way, and, after passing through potash, waj reduced by iron, 

 \ copper not being sufficiently active, at least without a very high 

 temperature. The iron was prepared from blacksmith's scale. 

 In order to get quit of carbon, it was first treated with a cirren; 

 of oxygen at a red heat, and afterwards reduced by hydrogen, 

 the reduction being repeated after each employment. The 

 greater part of the work of reducing the gas was performed out- 

 side the furnace in a tube heated locally with a Bunsen fliine. 

 In the passage through the furnace in a tube containing similar 

 iron, the work would be completed, if necessary. Next followed 

 washing with sulphuric acid (as required in the ammonia pro- 

 cess), a second passage throuijh the furnace over copper oxide, 

 and further washing with sulphuric acid. In order to obtain 

 an indication of any unreduced nitric oxide, a wash-bottle con- 

 taining ferrous sulphate was introduced, after which f.lloived 

 th; Nesslertest and drying tubes, as already described. .\s 

 thus arranged, the apparatus could be employed without altera- 

 tion, whettierthe nitrogen to be collected was derived from air, 

 from ammonia, from nitric oxide, from nitrous oxide, or from 

 ammonium nitrite. 



The numbers which follow are the weights of the gas con- 

 tained by the globe at zero, at the pressure defined by the man j- 

 meter when the temperature is 15°. They are corrected for the 

 errors in the weights, but not for the shrinkage of the globe 

 when exhausted, and thus correspond to the number 2"3I026, 

 as formerly given for niirogen. 



Nitrogen from NO by Hot Iron 



November 29, 1S93 ... 2 ■30143"! 



December 2, 1893 ... 2'2989oKj 



Decembers, 1893 ... 2'298i6|" 



December 6, 1893 ... 2"30l82j 



Nitrogen from NnO by Hot Iron. " 

 December 26, 1893 ... 2-29S69 / ., 



ean, 2'iOOoS 



December 28, 1893 



2 29940 ) 



ean, 2 '29904 



Nitrogen from Ammonium Nitrite passed over Hot Iron. 



January 9, 1894 2-298491 ,,.„ ,-,0860 



January 13, 1S94 2-29889.( '^'^''"' ^ ^9»b9 



With these are to be compared the weights of nitrogen derived 

 from the atmosphere. 



Nitrogen from Air by Hot Iron. 



December 12, 1893 

 December 14, 1893 

 December 19, 1893 

 December 22, 1893 



231017 ^ 

 2 •30986(H) I 

 2-3ioo3(H) j 



Mean, 2'3I003 



■31007 



Nitrogen from Air by Ferrous Hydrate. 



January 27, 1894 2'31024'j 



January 30, 1894 2'3ioio [- Mean, 2'3io20 



February i, 1894 231028 j 



In the last case a large volume of air was confined for several 

 hours in a glass reservoir with a mixture of slaked lime and 

 ferrous sulphate. The gas was displaced by deo.\ygenated 

 water, and further purified by passage through a tube packed 

 with a similar mixture. The hot tube-, were not used. 



If we bring together the means for atmospheric nitrogen 

 obtained by various methods, the agreement is seen to be good, 

 and may be regarded as inconsistent with the supposition of 

 residual oxygen in quantity sufficient to influence the weights. 



.Atmospheric Nitrogen. 



By hot copper, 1892 2'31026 



By hot iron, 1S93 2'3ioo3 



By ferrous hydrate, 1894 2'3I020 



Two of the results relating to hot iron, those of December 14 

 and December 19, were obtained from nitrogen, into which 

 hydrogen had been purposely introduced. An electrolytic 

 generator was inserted between the two lubes containing hot 

 iron, as formerly described. The generator worked under its 

 own clcctriimolive force, and the current was measured by a 

 tangent galvanometer. Thus, on December 19, the dcllsction 

 throughout the time of filling was 3', representing about i/lS 

 ' The N^O was prepared from zinc and very dilute nitric acid. 



