APPENDIX III; 493 



through the porous material.. It remained, therefore-, to separate this im- 

 purity from the nitrogen. To do this Rayleigh and Ramsay adopted two 

 methods, converting the nitrogen into solid and liquid substances, either, 

 by absorbing the nitrogen by heated magnesium (Chapter V., Note 6, and 

 Chapter XIV., Note 14), with the formation of nitride of magnesium, or else- 

 by converting it into nitric, acid by the action of electric sparks or the presence 

 of an excess" of air and alkali, as in Cavendish's method. 3 bis In both cases 

 the nitrogen entered into reaction, while the heavier gas mixed with it 

 remained inert, and was thus able to be isolated. That is", the argon could be 

 separated by these means from the excess of atmospheric nitrogen accom- 

 panying it. 4 As an illustration, we will describe how argon was obtained 

 from the atmospheric nitrogen by means of magnesium. 5 To begin with, 

 it was discovered that when atmospheric nitrogen was passed through a tube 

 containing metallic magnesium heated to redness,' its specific gravity rose to 

 14'88. As this showed that part of the gas was absorbed by the magnesium, 

 a mercury gasometer filled with atmospheric nitrogen was taken, and the 

 gas drawn over soda-lime, P 2 5 heated magnesium 6 and then through 

 tubes containing red-hot copper oxide, soda-lime and phosphoric anhydride 

 to a second mercury gasometer.. Every time the gas was repassed through 

 the tubes, it decreased in volume and increased in density. After repeating 



of the metals, like PeO) besides red-hot copper, and that the nitrogen obtained is always 

 just as heavy. Besides which, nitrogen is also set free from its oxides by copper, and the 

 nitrogen thus obtained is lighter. Therefore it is not the copper which produces the 

 .heavy gas i.e. argon. 



8 bis 1$ j a worthy 'of note that Cavendish obtained a small residue of gas in con- 

 verting nitrogen into nitric acid ; but he paid no attention to it, although probably he 

 had in.his hands the very argon recently discovered. 



4 When in these experiments, instead of atmospheric nitrogen the gas obtained from 

 its compound was taken, an inert residue of a heavy gas, having the properties of argon, 

 was-also remarked, but its-amount was very small. Eayleigh and Ramsay ascribe the 

 formation of this residue to the fact that the gas in these experiments was collected over 

 water, and $ portion of the dissolved argon in it might have passed into the nitrogen. As 

 the authors of this supposition did not prove it by any special experiments, it forms a 

 weak point in their classical research. If it be admitted that argon is N 3 , the fact of its 

 being obtained from the nitrogen of compounds might be explained by the polymerisation 

 of a portion of the nitrogen in the act of reaction, although it is impossible to refute 

 Eayleigh and Eamsay's hypothesis of its being evolved from the water employed in the 

 manipulation of the gases. Three thousand volumes of nitrogen extracted from its 

 compounds gave about three volumes of argon, while thirty volume's were yielded by the 

 eame amount of atmospheric nitrogen. 



6 The preparation of argon by the conversion of nitrogen into nitric acid is complicated 

 by the necessity of adding a large proportion of. pxygen and alkali, of passing jin electric 

 discharge through the mixture #>r a long period, and then removing the remaining' 

 oxygen. AlLthis was repeatedly done by the authors, but this method is far more 

 complex, both in practice and theory, than the preparation of argon by means of 

 magnesium. From 100 volumes of air subjected to conversion into HN0 3 , 0'76 volume 

 of argon were obtained after absorbing the excess of oxygen. 



6 In these and the following experiments the magnesium was placed in an ordinary 

 hard glass tube, and heated in a gas furnace to a temperature almost sufficient to soften 

 the glass. The current of gas must be very slow (a tube containing a small quantity of 

 sulphuric acid served as a meter), as otherwise the heat evolved in the formation of tho 

 Mg 3 N 2 (Chapter XTV., Note 14) will melt the tube. 



